Jump to content

Requests for technical support from the VASP team should be posted in the VASP Forum.

Thermodynamic integration: redox potential: Difference between revisions

From VASP Wiki
Csheldon (talk | contribs)
Csheldon (talk | contribs)
No edit summary
Line 1: Line 1:
[[Thermodynamic integration|Thermodynamic integration (TI)]] can be used to combine two different methods through the integration, e.g., [[:Category:Machine-learned force fields|machine-learned force fields]] (MLFFs) and [[:Category:Exchange-correlation functionals|GGA]] functionals, or GGAs and [[:Category:Hybrid functionals|hybrid functionals]]. It is also possible to integrate between two different states of the same system, e.g., a redox couple such as Fe<sup>3+</sup>/Fe<sup>2+</sup> to obtain the redox potential.
== Introduction ==
In this article, the procedure of Jinnouchi et al. {{Cite|jinnouchi:karsai:2024}} to calculate the redox potential of an electrochemical half-cell, following the example of the Fe<sup>3+</sup>/Fe<sup>2+</sup> half-cell reaction (''oxidized state/reduced state''):
In this article, the procedure of Jinnouchi et al. {{Cite|jinnouchi:karsai:2024}} to calculate the redox potential of an electrochemical half-cell, following the example of the Fe<sup>3+</sup>/Fe<sup>2+</sup> half-cell reaction (''oxidized state/reduced state''):


Line 17: Line 13:
where U<sub>0</sub> and U<sub>1</sub> are the potential energies of the non-interacting and interacting (''reduced'') states, respectively, &lambda; is a coupling parameter, &mu; is the chemical potential (relative to vacuum), and ''n'' is the number of electrons in the half-cell reaction.
where U<sub>0</sub> and U<sub>1</sub> are the potential energies of the non-interacting and interacting (''reduced'') states, respectively, &lambda; is a coupling parameter, &mu; is the chemical potential (relative to vacuum), and ''n'' is the number of electrons in the half-cell reaction.


The following ''non-interacting'' (&lambda;=0) and ''interacting'' (&lambda;=1) pairs are used:
== Outline ==
The first step is to describe [[Construction:Training_MLFF_for_redox_reactions#Training_of_water_slab|preparation of machine-learned force fields (MLFFs) for the redox pair and water slab]]. The [[Construction:Vacuum reference|chemical potential relative to the vacuum]] <math>\mu n</math> is then calculated via the difference in local potential <math>e  \Delta \bar{\phi}</math>. This allows comparison between the computational and experimental half-cells.


Three thermodynamic integrations are described from ''non-interacting'' (&lambda;=0) to ''interacting'' (&lambda;=1) systems:
{|cellpadding="5" cellspacing="0" border="1"
{|cellpadding="5" cellspacing="0" border="1"
| '''TI'''
| '''TI'''
Line 38: Line 36:
|}
|}


Due to the high cost of converting from RPBE to PBE0, we omit describing thermodynamic perturbation theory (TPT):
Though described in the paper, due to the high cost of converting from RPBE to PBE0, we omit describing thermodynamic perturbation theory (TPT):
* From RPBE+D3 to PBE0 (Fe<sup>3+</sup>)
* From RPBE+D3 to PBE0 (Fe<sup>3+</sup>)
* From RPBE+D3 to PBE0 (Fe<sup>2+</sup>)
* From RPBE+D3 to PBE0 (Fe<sup>2+</sup>)
{{NB|tip|TPT can be replicated using &Delta;-learning from RPBE to PBE0, using the same procedure as from MLFF to RPBE.}}
{{NB|tip|TPT can be replicated using &Delta;-learning from RPBE to PBE0, using the same procedure as from MLFF to RPBE.}}


The [[Construction:Vacuum reference|chemical potential relative to the vacuum]] <math>\mu n</math> is calculated via the difference in local potential <math>e  \Delta \bar{\phi}</math>. This allows comparison between half-cells and with experiment. Finally, [[Construction:Training_MLFF_for_redox_reactions#Training_of_water_slab|preparation of machine-learned force fields (MLFFs) for the redox pair and water slab]] is also described.
Finally, the redox potential and absolute redox potential (relative to the standard hydrogen electrode SHE) are calculated and, alongside the constituent terms, are compared to literature.


== Input files ==
== Input files ==

Revision as of 13:41, 11 August 2026

In this article, the procedure of Jinnouchi et al. to calculate the redox potential of an electrochemical half-cell, following the example of the Fe3+/Fe2+ half-cell reaction (oxidized state/reduced state):

[math]\displaystyle{ \mathrm{Fe^{3+} + e^- \;\rightleftharpoons\; Fe^{2+}} }[/math]

The following two models are used:

  • [math]\displaystyle{ [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_n]^{3+} }[/math] - Fe ion in 64 H2O bulk cell with 3 valence electrons put in the background charge
  • [math]\displaystyle{ [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_n]^{2+} }[/math] - Fe ion in 64 H2O bulk cell with 2 valence electrons put in the background charge

Thermodynamic integrations (TIs) are used to calculate the free energy difference ΔA using the following basic equation:

[math]\displaystyle{ \Delta A = \int_0^1 \langle U_1 - U_0 \rangle_{\lambda} d\lambda - \mu n }[/math]

where U0 and U1 are the potential energies of the non-interacting and interacting (reduced) states, respectively, λ is a coupling parameter, μ is the chemical potential (relative to vacuum), and n is the number of electrons in the half-cell reaction.

Outline

The first step is to describe preparation of machine-learned force fields (MLFFs) for the redox pair and water slab. The chemical potential relative to the vacuum [math]\displaystyle{ \mu n }[/math] is then calculated via the difference in local potential [math]\displaystyle{ e \Delta \bar{\phi} }[/math]. This allows comparison between the computational and experimental half-cells.

Three thermodynamic integrations are described from non-interacting (λ=0) to interacting (λ=1) systems:

TI λ=0 λ=1
MLFF:MLFF oxidized (Fe3+) reduced (Fe2+)
MLFF:GGA MLFF (Fe3+) RPBE+D3 (Fe3+)
MLFF:GGA MLFF (Fe2+) RPBE+D3 (Fe2+)

Though described in the paper, due to the high cost of converting from RPBE to PBE0, we omit describing thermodynamic perturbation theory (TPT):

  • From RPBE+D3 to PBE0 (Fe3+)
  • From RPBE+D3 to PBE0 (Fe2+)

Finally, the redox potential and absolute redox potential (relative to the standard hydrogen electrode SHE) are calculated and, alongside the constituent terms, are compared to literature.

Input files

POSCARs

The chemical potential requires four different systems: bulk H2O with 64 molecules (64H2O_bulk), Fe3+ in 64 H2O (Fe3P_64H2O), Fe2+ in 64 H2O (Fe2P_64H2O), H2O slab with 128 molecules (128H2O_slab). I.e., a bulk water reference, [math]\displaystyle{ [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_n]^{3+} }[/math], [math]\displaystyle{ [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_n]^{2+} }[/math], and the water slab.

Figure 1. Top left: Fe3+ in 64 H2O (Fe3P_64H2O), top center: Fe2+ in 64 H2O (Fe2P_64H2O), top right: bulk H2O with 64 molecules (64H2O_bulk), and bottom: H2O slab with 128 molecules (128H2O_slab).
Click to reveal the 64H2O_bulk POSCAR
Water
1
     12.42128700       0.00000000       0.00000000
      0.00000000      12.42128700       0.00000000
      0.00000000       0.00000000      12.42128700
H  O
  128    64
Direct
      0.36257633       0.37953597       0.67785342
      0.42947178       0.43286249       0.59010358
      0.66870393       1.13989162       0.58842641
      0.70823249       1.22041509       0.67807457
      0.35637008       0.05839855       0.21517466
      0.44580288       0.01834909       0.16004703
      0.44380894       0.67759921       0.05971511
      0.44857483       0.64047308       0.17235572
      1.14522157       0.76633728      -0.07286828
      1.26197238       0.78911446      -0.10391832
      0.56790416       1.14251886       0.92143084
      0.60754105       1.14691841       0.80551737
      0.75633099       0.25670520       0.32073462
      0.75786987       0.15087192       0.26471573
      0.74642803      -0.03671116       1.07026855
      0.68277568      -0.08917103       1.16765095
      0.08323566      -0.02515907      -0.01412446
     -0.00880432       1.02342521       0.04212898
      0.68157988       0.24579303       0.03134658
      0.60083186       0.23578159       0.12220439
      1.14251010       0.79368279       0.23822678
      1.03381447       0.81936982       0.30217442
      1.45625953       0.82211861      -0.39364182
      1.33249296       0.84676639      -0.38681569
      0.73773505       0.37233458       0.47040761
      0.62289024       0.34929795       0.43767209
      0.63992674       0.70350215       0.78737637
      0.67764626       0.66562038       0.90017103
      0.38737624       0.10112290       0.97816413
      0.44041019       0.20087678       1.04654040
     -0.74229635       0.27326641       0.85574288
     -0.86480570       0.30089547       0.83717409
      0.98781733       0.58627453       1.16338342
      0.98642719       0.45910015       1.19257026
      0.32814541       0.15987161       0.50362237
      0.25642761       0.26648016       0.48295405
      0.69811093      -0.56389784       0.28108666
      0.70770558       0.42946360       0.15518042
      0.18565685       0.52373867       0.56827259
      0.08659439       0.58375638       0.51565848
      0.44991203       0.27342036       0.48425454
      0.55101593       0.27228106       0.56380912
      0.41624326      -0.17788427       0.80896103
      0.50257275      -0.21360866       0.89707634
      0.28998176       0.48372062      -0.01768589
      0.19491021       0.39742192      -0.01269715
      1.06654096       0.36410409       0.63682306
      1.03975716       0.44960909       0.73041188
      0.50170068       1.61380686       0.40736049
      0.49942205       1.73793230       0.43266624
      0.37390409       0.30295427       0.17857302
      0.34033093       0.38510006       0.09520283
      0.30807694       0.20122962       0.31494909
      0.22529499       0.19805563       0.21739075
      1.12308748       0.37150659       0.42477646
      1.06276778       0.26307066       1.46962386
     -0.15792914       0.29610530       0.85397054
     -0.07308234       0.27252743       0.77021418
      0.85228948       0.16062637       0.95526886
      0.89963468       0.18253764       1.06178327
      0.19181780       0.04626484      -0.19418583
      0.15189262      -0.06556287      -0.18492234
     -0.10238306       0.45933074       0.94465075
      0.78170215       0.43034159       0.95991840
     -0.04726476       0.53527628       0.38000776
     -0.10379563       0.60547798       0.46538564
     -0.00098972       1.02353900       0.73537767
     -0.10239174       1.10640574       0.72833236
      0.83303676       0.93517612       0.67263678
      0.72416689       0.88061601       0.69336360
      0.83396381       0.79727679       0.33276158
      0.84935945       0.89986765       1.25490788
      0.43767040       0.26474088       0.82690407
      0.40610758       0.19731651       0.73463453
     -0.22521691       0.99033821       0.52178482
     -0.21732111       1.08901868       0.43461921
      0.55979128       0.65441008       0.58905315
      0.51739017       0.64402769       0.70843828
      1.15263203       0.22553743       1.04375491
      1.05410314       0.23287904       1.11317058
      0.40787600       0.01178034       0.65057706
      0.46239323       0.06947748       0.55789921
      1.22298533      -0.28915950       0.52942510
      0.19053464      -0.18268639       0.46366419
      0.34645899       0.68043144       0.72737986
      0.36594763       0.55141902       0.69243633
      0.56017599       0.33134538      -0.03087852
      0.61388449       0.39021229      -0.12522124
      0.38664251      -0.13040994      -0.70002278
      0.35405937      -0.19423015      -0.59774517
      0.73338812       0.70036370       0.46781396
      0.80345417       0.77305746       0.53896313
      0.70280496       0.86052960       0.87581100
      0.72653862       0.98582519       0.88541416
      0.94986235       0.10516542       0.53628061
      0.99735924       1.10316818       0.41487930
      0.34586913       0.92208748      -0.04377027
      0.27835954       0.97034641       0.04814922
      0.88788268       1.29429166       0.20459804
     -0.10649273       1.36074553       0.09165817
      0.39371787       0.57519096      -0.11020542
      0.46220136       0.48981436      -0.05946583
      0.89286511       0.79370028       0.86701692
      0.96099685       0.84339162       0.96334218
      0.62514345       0.53133485       0.73825559
      0.73640530       0.50006566       0.71024894
     -0.12902917       0.72677131       1.16320660
     -0.11814514       0.70432566       1.03349629
      1.01129606       0.61898608       0.90675712
      1.09968460       0.53447870       0.92387699
     -0.14457334       0.35937352       0.63141164
     -0.11499539       0.45568803       0.54735066
      0.48813670       0.98589446       0.40760031
      0.60110088       1.02927414       0.43954578
     -0.37236788       0.57165925       0.04667849
     -0.24946342       0.60016434       1.06579556
      1.07450858       1.10382861       0.26264566
      1.12554235       0.99644744       0.31325744
      0.62490856       0.06519849       0.18845978
      0.54885406       0.10569865       0.28792416
      0.55694560      -0.17713139       0.27541275
      0.56084272      -0.21506154       0.16885793
      0.12891427       0.50587770       0.28000948
      0.23833432       0.43434745       0.29542543
      1.48346125       0.46743806       0.19449182
      1.57481458       0.52369865       0.24680216
      0.17873553       0.62275568       0.11942301
      0.26852366       0.68872043       0.07818815
      0.35693455       0.43925319       0.62530196
      0.64792950       1.20400828       0.63184735
      0.39412198      -0.01057009       0.20787038
      0.43581616       0.71008914       0.13099142
      1.19397105       0.77903373       0.85946991
      0.63615555       1.12938446       0.87822715
      0.80661353       0.20330608       0.29232873
      0.73246578      -0.02838354       1.14624509
      0.03244721      -0.04025903       0.03944908
      0.63721217       0.28885881       0.08035039
      1.11493495       0.82738114       0.30859190
      1.39883698       0.85058088      -0.34459284
      0.69698494       0.36107968       0.40464588
      0.64192914       0.72485162       0.86089438
      0.45396944       0.13747103       1.00222318
     -0.81120011       0.28079526       0.89372357
      1.01585028       0.52957121       1.21343372
      0.31821591       0.22470258       0.45731626
      0.70888882      -0.51685513       0.22019861
      0.13832317       0.58769764       0.57254578
      0.51028551       0.31315460       0.51155010
      0.42617734      -0.19946999       0.88578770
      0.21795347       0.46397897       0.02254897
      1.03345078       0.37392845       0.70810584
      0.53447426       1.66561969       0.45708230
      0.40848000       0.35179327       0.12578669
      0.30420794       0.19684477       0.23570844
      1.10944135       0.32634895       1.48853144
     -0.15068923       0.25159638       0.78858129
      0.84350236       0.13666558       1.03077541
      0.12621458       0.00799599      -0.18726449
     -0.14969491       0.39803889      -0.04386545
     -0.05257019       0.54926511       0.45604016
     -0.07042394       1.04132825       0.69759096
      0.77456016       0.89777696       0.63596725
      0.87893918       0.82791839       1.27826204
      0.37199961       0.24693838       0.78669458
     -0.26629559       1.03776777       0.47472997
      0.58383474       0.64578572       0.66290779
      1.11758097       0.18829015       1.10755225
      0.41441089       0.08360444       0.62404569
      0.25236886      -0.21779138       0.50357805
      0.38654211       0.61365045       0.74790977
      0.54189953       0.36543129      -0.10123356
      0.41572204      -0.15596095      -0.63075239
      0.80055913       0.73724417       0.46650168
      0.76508964       0.91308708       0.87755337
      0.94189130       0.13529024       0.46400834
      0.29460037       0.97883985      -0.02591476
     -0.06126178       1.32786996       0.14953350
      0.41172576       0.54824212      -0.03901993
      0.94501130       0.77310663       0.92132598
      0.69302524       0.50734691       0.77446848
     -0.13207205       0.66750977       1.10613301
      1.02911948       0.53980433       0.89023275
     -0.17248923       0.40767816       0.57425135
      0.52217208       1.04992599       0.43651343
     -0.30113028       0.57147331       0.01268190
      1.11295226       1.07452050       0.32297073
     -0.41735391       0.12325009       0.21804170
      0.61116931      -0.19691698       0.22556446
      0.17536968       0.46512423       0.32953214
      1.49704038       0.52822279       0.24728978
      0.19113993       0.69295724       0.10392182
Click to reveal the Fe3P_64H2O POSCAR
Fe_64H2O
1
     12.42282200       0.00000000       0.00000000
      0.00000000      12.42282200       0.00000000
      0.00000000       0.00000000      12.42282200
H  O  Fe
  128    64     1
Direct
     -0.38272023       0.47236734       0.69895078
     -0.27203601       0.41866794       0.72914269
      0.60916541       0.72796225       0.09306829
      0.71070494       0.78725068       0.14392771
      1.08865564       0.93820602       0.24600432
      1.03755512       0.98120737       0.35350048
      0.04276558       1.23801733       0.56678300
      0.45616640       0.36926572       0.39344586
     -0.16977976       0.40716591       0.53863440
     -0.25237329       0.38130525       0.44755164
      0.44169261       1.14516978       0.14529032
      0.37457743       1.13530301       0.24819417
      0.18407518       0.25222959       0.06812304
      0.09998538       0.14744161       0.06444770
      0.27831295       0.57479968       0.31380844
      0.29633366       0.45926581       0.36724418
      0.64763154      -0.53184911       0.87002912
      0.63022496       0.40977773       0.99107908
      0.47906160       0.58853267       0.63100265
      0.59945353       0.62329058       0.64816927
      0.87712851       0.41898140       1.07505748
      0.26314503      -0.13253460       0.01243951
      0.16153170      -0.19745195       0.05804701
      0.34412600      -0.01810085       0.81692911
      0.14554222       0.77130921      -0.25213594
      0.21209078       0.79452634      -0.14442072
      0.41500251       0.04461290       0.96837924
      0.49008610       0.14359786       0.93019679
      0.82125847       0.86254586       1.27147476
      0.00873717       0.10267666       0.23211446
      0.35980746       0.34237108       0.76169366
      0.33485343       0.46345006       0.77046483
      0.90320251       0.61221204       0.04264507
      0.97690745       0.71802735       1.06017819
      0.96030764       0.81465128       0.70019704
      1.01749178       0.74674122       0.60432752
      0.64007416       0.23981183       0.92947124
      0.31788389      -0.12374136       0.74827741
      0.99321033       0.93631524       0.55767630
      0.15487454       0.51028490      -0.09542554
      0.66815917       0.79686891       0.72718580
      0.76202793       0.70002522       0.75366280
      0.13591369      -0.02901335       0.00566347
      0.08957800       1.06396642      -0.07143824
      0.53392446      -0.11896063       0.23953882
      0.48718378      -0.00799262       0.25860106
     -0.07163033       1.26809135       0.50762252
      0.67405502       0.12105566       0.95083205
      0.74551359       0.62681866       0.34775553
      0.66650260       0.64357368       0.25540936
      0.38872827       0.12804968       0.55656518
      0.33782256       0.21579745       0.49248801
      0.92231233      -0.04307885       1.00089073
      0.79411522      -0.04854941       1.01531498
     -0.40705912       1.12847907       0.48347215
      0.65420892       1.23981902       0.47957005
      0.84599640      -0.09249550       0.84023452
      0.80327236       0.97997213       0.74592535
      0.88638541       0.47237368       0.72110537
      0.88941805       0.35493190       0.74249811
      0.55296221       0.93428417       0.55243420
      0.51441228       0.92952738       0.43767406
      0.73847683       0.51634987       1.03266322
      0.40092134       0.63952229      -0.01737781
      0.41176789       0.89134362       1.10615330
      0.44444253       0.84405868       0.99393367
      0.58073572       0.63347610      -0.04423652
      0.60854638       0.72933752      -0.11607112
     -0.16580359       0.22001380       0.89963070
     -0.04391612       0.21085677       0.85654400
      0.40533602       0.50000334       0.11555470
      0.34998095       0.38355577       0.10448457
     -0.24359234       0.77537730       0.45894937
     -0.26614437       0.70560002       0.56106171
      0.28303298       0.61126441       0.01597951
      0.37578327       0.33380444       0.30290136
      0.59618764       0.27699048       1.12423906
      0.50319683       0.35108728       1.09799129
      0.18989659       0.76741117       1.22566037
      0.06153560       0.75549602       0.22936925
      0.51785592       0.24354330       0.65223118
      0.56708719       0.32005973       0.73245604
      0.61206395       0.98022340       0.70759384
      0.50678625       0.91620503       0.71723010
      0.68602440       0.14707860       0.76412395
      0.69294218       0.12172781       0.64036372
      0.33488986       0.71525634       0.14956129
      0.35814895       0.80854785       0.22920363
      0.95945912       1.05245660       0.53679791
      0.77994512       0.55222218       1.15138214
      0.69626269       0.94689443       0.43758767
      0.82244291       0.95270203       0.44158402
     -0.08533410       0.30668689       0.99691887
      0.88689642       0.15254779       0.21721075
      0.96565778       0.66203563       0.74352603
      0.91899641       0.64391575       0.86105003
      0.60192845       0.32627053       0.34541527
      0.54412777       0.22739074       0.29056180
      0.33801876       0.24481339      -0.03610605
      0.27498242       0.34868783      -0.07124872
      0.63970642       0.49240211       0.35877270
      0.61552019       0.46892953       0.48438447
      0.30584874       0.64699933      -0.22951580
      0.42787645       0.64881697      -0.19623458
      0.05975532       0.12314654       0.75074831
     -0.02832220       1.03112946       0.76086242
      1.07382577       0.25251612       0.39457391
      1.17074101       0.24004400       0.30909053
      0.90882853       0.66787644       0.52270722
      0.07399163       0.59412808       0.95304999
      0.13906082       0.47905225       0.10518101
      1.17121656       0.46180650       0.23562581
      0.97971011       0.63429872       0.37278291
      0.90631471       0.68858591       0.26904690
      0.60516786       0.96463888       0.06395544
      0.68233031       1.04347277       1.12012494
      0.20897747       0.21380315       0.63498998
      0.20507421       0.29490009       0.72649781
      0.21069366       1.05104536      -0.68658423
      0.27938942       1.09406910       0.40078460
      0.70263174       0.14455648       1.25970691
      0.75730930       0.04722448       1.29768294
      0.91307779       0.40130091       0.34978752
      0.94369056       0.50994390       0.28013594
      0.08933991       0.43228293       0.60852163
      1.17837154       0.48628664       0.53072146
      1.00504493       0.58007882       0.54073092
      0.86291931      -0.13828811       1.15173275
     -0.34491075       0.43621986       0.75416516
      0.63900568       0.75492759       0.15829659
      1.07199795       1.00257563       0.28363155
      0.38420131       0.34485841       0.37967695
     -0.17342306       0.37643136       0.46438657
      0.45349630       1.14005000       0.22505348
      0.11869813       0.21939929       0.09604324
      0.23622993       0.50759344       0.33909324
      0.64875252       0.47771851       0.95286519
      0.55590506       0.57693205       0.60050819
      0.18736673      -0.15437724      -0.00677806
      0.37523088      -0.06818877       0.76435686
      0.21811495       0.76245384      -0.22055952
      0.42220970       0.12606004       0.96558981
      0.85780135       0.81574581       1.21531426
      0.30433544       0.39124488       0.77849745
      0.95758533       0.65697710       1.00747411
      1.03085555       0.79681957       0.66923251
      0.69067343       0.18643375       0.90833405
      0.96523126       0.16955239       0.22035170
      0.68612747       0.72230731       0.74299918
      0.08987161       0.03581255       0.00348357
      0.46357734      -0.08420990       0.24196675
     -0.01222913       1.21468404       0.51335175
      0.71162904       0.58691114       0.28804098
      0.32268708       0.16090339       0.53975026
      0.86234882      -0.08436224       0.98773807
     -0.38355188       0.19092778       0.52248232
      0.85291582      -0.08281162       0.75894361
      0.86323773       0.40597333       0.69118967
      0.54292990       0.98123241       0.48667605
      0.80728528       0.53397589       1.07560692
      0.39528125       0.89790682       1.02768167
      0.56047647       0.70886600      -0.05694049
     -0.09585039       0.25981162       0.89091800
      0.40071565       0.42814971       0.14908255
     -0.23238312       0.70278251       0.48864911
      0.35169257       0.62880569       0.04279978
      0.56212715       0.31299799       1.06345122
      0.12066294       0.79773619       1.19966391
      0.51154081       0.26173878       0.72839369
      0.58450605       0.90652737       0.69203180
      0.70957535       0.09399646       0.71195964
      0.32002783       0.74390105       0.22241023
      0.95247763       0.97831298       0.50380136
      0.76168681       0.93342180       0.39565898
     -0.07590969       0.35133103       1.07020111
      0.90649162       0.63028257       0.78114555
      0.61524001       0.25974801       0.30414551
      0.30266553       0.31064613      -0.00899828
      0.62120647       0.43621160       0.41233540
      0.36878355       0.59976322      -0.20951626
      0.00592307       0.09406140       0.79582533
      1.10947213       0.28743919       0.33114811
      0.13898678       0.54360995       0.97023057
      1.15168897       0.42574337       0.16437693
      0.96099089       0.62982868       0.29120309
      0.66514203       1.00695060       0.04564722
      0.15635030       0.24896214       0.68388955
      0.26078411       1.11001890       0.32632346
      0.75255117       0.09346553       1.23417762
      0.93550375       0.42521425       0.27361930
      1.12555194       0.49730673       0.58995753
      0.97951694       0.64650296       0.50479031
      1.02535902       0.32276265       0.18627127
Click to reveal the Fe2P_64H2O POSCAR
Fe_64H2O
1
     12.42282200       0.00000000       0.00000000
      0.00000000      12.42282200       0.00000000
      0.00000000       0.00000000      12.42282200
H  O  Fe
  128    64     1
Direct
      0.12743711       0.48760461       0.68402834
      0.07224030       0.59099573       0.69720079
      0.39623895       0.90251919      -0.68562329
      0.52396846       0.89222892      -0.69202626
      0.42964083       0.63656491       0.92024856
      0.40471536       0.51747508       0.92244566
      0.50949529       0.22553243       0.82975356
      0.79695561      -0.29210416      -0.14766098
      0.00805766       0.01676094       0.93033834
     -0.01969191       0.14077136       0.89733509
      0.01773692       1.49221026      -0.45662142
     -0.09754205       1.45083180      -0.48707747
      0.28568895       0.07977712       0.14809775
      0.40460027       0.11889958       0.12632577
     -0.44823614      -0.23392047       0.91065326
     -0.44655395      -0.27382665       1.03236410
      0.55758309       0.63486700       0.51461921
      0.54015662       1.52364880       0.45450703
      0.67045916       0.85136844       0.58289035
      0.71164261       0.89435637       0.47626762
      1.16684705       0.13193713       0.89590371
      0.33871812       0.20748811       0.69296855
      0.38041592       0.31864036       0.75378916
     -0.26840230      -0.60381695       0.57433173
      0.25751301       1.09723808      -0.39131073
      0.28561906       1.17135043      -0.49010853
     -0.15559770       0.77405954       1.51947552
     -0.03350167       0.77676575       1.52339975
      0.75237735       1.02309221       1.12180723
      0.04826055       0.15234086       0.05862687
     -0.09230147      -0.06114088       1.02402855
     -0.07779336      -0.14013315       0.92524744
      0.68560087       0.63322667       1.36320530
      0.79400335       0.69800156       2.34722324
      1.01111679       0.16477327       0.53663862
      0.98618018       0.28565957       0.49809698
      0.20452861       0.81136804       0.83127978
     -0.29824646      -0.48415938       0.54811270
      0.37502040       1.26549068       0.41257460
      1.30154976       0.64025841       0.11667748
      1.75290818       0.59403116       0.98316689
      1.65052923       0.63412803       0.91547295
      0.75375838       0.00138371      -0.37473678
      0.76130867       1.05807834      -0.25911110
     -0.05696647      -0.29493528       0.76468746
      0.02811791      -0.33267590       0.85098776
      0.61065413       0.29830310       0.85951557
      0.11763966       0.86822584       0.90729729
      0.18919114       0.55109134       0.38993918
      0.21099928       0.52226945       0.51012484
      0.03269714       0.36292005       0.33650725
      0.02620788       0.48115860       0.28181401
      1.05541232       0.90157404       0.64524915
      1.07849658       0.77961507       0.68820380
     -0.62352298       1.63205141       0.30877689
      0.43788457       1.73907737       0.26620496
      0.64515164      -0.84752695       1.12986454
      0.64730542       0.18633377       1.26064334
      0.19923207      -0.08426170       0.07502044
      0.22493320      -0.20749942       0.08281964
      0.78950677       1.18291196       0.57758905
      0.83466268       1.23338961       0.48038196
      1.10490483       1.28683406       0.74494774
      0.29928808       0.66864147      -0.17842015
      0.69120317       0.84829619       1.11035412
      0.67223805       0.75611954       1.18775106
     -0.00106366       0.61277354       0.38525072
      0.01326608       0.68609575       0.28998127
     -0.07137268       0.05723237       0.64512696
      0.03262162       0.06902330       0.71661499
      0.77907316       0.40440365       0.75246685
      0.73437154       0.47097142       0.84530449
      0.22165260       0.78128841       0.57222522
      0.24873347       0.68762843       0.48624453
      0.21948415       0.65300265      -0.26571256
      0.79089209      -0.20809083      -0.24704170
      1.11107834       0.01381845       0.32957265
      1.03239487       0.10538648       0.35890625
     -0.22306466       1.43601128       1.11757892
     -0.24593929       1.53904148       0.17695298
      0.53330947      -0.13832394       0.74775872
      0.48380538      -0.08752260       0.84569979
      0.33958593       1.05428999       0.90703938
      0.29513801       0.93047632       0.90464110
     -0.10080201      -0.17071890       0.20726349
      0.00812468      -0.20258160       0.13847835
      0.08102303       0.64583254       0.03494449
     -0.04079584       0.61193214       0.04209357
      0.35121443       1.17006312       0.32377652
      1.18017291       1.28895470       0.63748305
      0.44815316       0.76165600      -0.42603898
      0.46425067       0.68605942      -0.32598380
      0.26710057       0.21583209       0.85066344
      1.08895608       0.13400129       0.17359061
      0.65188184       1.12136051       0.88104293
      0.65005020       0.99400031       0.86041374
      0.74276310       0.93357167       0.31617568
      0.65193906       1.01050888       0.33337941
      0.22155564      -0.06334224      -0.33974479
      0.31584241      -0.05457389      -0.25072038
      0.46701413       0.39534529       0.33741153
      0.37353168       0.43618379       0.40490478
      0.88534124       0.31114574       0.85608235
      0.90593210       0.27739909       0.97341481
      0.39857237      -0.04387750       0.56182123
      0.47095275       1.02320312       0.49993905
      1.25892990       0.45837652       0.17875477
      1.15656687       0.39089427       0.22252886
      0.51644837       0.17070272       0.40580457
      1.27940834       0.60940694       0.99753791
      0.42616197       0.40350440       0.06681017
      1.44539498       0.30393771      -0.01376590
      0.46562325       1.01534518       0.03284939
      0.50319974       0.99064681       0.15470387
      0.81037140       0.25082530       0.14657752
      0.90914722       0.31376690       1.17885883
      0.90887977       0.86774057       1.39942038
      0.94187889       0.97203833       1.33441155
      0.22890408       0.88765248       0.26506994
      0.22943934       0.87502350       1.39740388
      0.49252993       0.56873322       1.17531223
      0.58322974       0.47973985       1.18073167
      1.07353906       0.35801775      -0.07352972
      1.10345201       0.46291908      -0.00569576
      0.56233028       0.47301291       0.65701182
      1.50111441       0.39245196       0.57504212
      0.64733050       0.17609466       0.44047892
      0.76155406      -0.00064089       0.99805907
      0.11696365       0.55392898       0.64536596
      0.45665944       0.88787932      -0.73431062
      0.37333616       0.58173353       0.89358570
      0.83287880      -0.23084103      -0.18836803
      0.03157586       0.08326143       0.89500066
     -0.01967168       1.44066290      -0.50120574
      0.32649692       0.14675159       0.14354441
     -0.47815402      -0.28476352       0.96183234
      0.58825114       1.58190086       0.46693607
      0.73530757       0.86486122       0.54696653
      0.36850393       0.23869519       0.76098331
     -0.24064441      -0.53169325       0.57977533
      0.24867886       1.17176032      -0.42128557
     -0.09114394       0.73086170       1.49415350
      0.77082046       0.96821649       1.06941593
     -0.03834292      -0.10477073       0.98185130
      0.72904928       0.67702858       2.31155822
      0.98643994       0.21068855       0.47648425
      0.18404121       0.88355581       0.86864094
      1.08703359       0.18844511       0.11444108
      1.71734102       0.59616846       0.90840384
      0.79123200       0.05674886      -0.33394462
      0.02043659      -0.31156425       0.77570162
      0.56069314       0.24338431       0.88537227
      0.24569014       0.53057214       0.44182948
      0.03448211       0.40131521       0.26357804
      1.09819988       0.83512130       0.63612042
     -0.60356192       0.67216851       0.24349363
      0.68641610      -0.81762609       1.18817124
      0.21611881      -0.14120573       0.12450673
      0.76919341       1.22245249       0.51393968
      1.14696413       1.32734585       0.69656507
      0.65811040       0.77819298       1.11522722
      0.04903142       0.62925399       0.32627031
      0.01260756       0.05983530       0.64228866
      0.74653920       0.39814097       0.82582336
      0.26593357       0.76215637       0.50729285
      0.25423481       0.71079817      -0.23075499
      1.04656732       0.05170956       0.30685598
     -0.27090311       1.50034802       1.11590884
      0.55144479      -0.10997314       0.82138721
      0.36595179       0.97842307       0.90355956
     -0.04879022      -0.22282940       0.18797022
      0.02303649       0.60374665      -0.00064438
      0.36248716       1.18806896       0.40233898
      0.50553342       0.72818132      -0.38174573
      0.23339102       0.17685431       0.91622715
      0.69519318       1.05764833       0.86986144
      0.66244443       0.93542605       0.32313623
      0.29157406      -0.03443908      -0.32197353
      0.43576289       0.39304384       0.41288487
      0.93290635       0.26807660       0.90192508
      0.46947458      -0.04604768       0.53317357
      1.23797107       0.38686102       0.19701795
      1.24279488       0.62426866       1.06753929
      1.39453671       0.36177382       0.00797544
      0.49872289       1.04632858       0.09816681
      0.86030136       0.31356352       0.11502915
      0.87609952       0.92053833       1.35250286
      0.23398309       0.92340184       1.33460122
      0.50301930       0.49047944       1.17320678
      1.13069333       0.39166539      -0.03166013
      1.52690177       0.40275423       0.64871882
      0.59258213       0.16054156       0.38717393
      1.22868038       0.27296875       0.05742047
Click to reveal the 128H2O_slab POSCAR
SYSTEM
1
     12.50000000       0.00000000       0.00000000
      0.00000000      12.50000000       0.00000000
      0.00000000       0.00000000      50.00000000
H  O
  256   128
Direct
     -0.15047607       0.45334683       0.32730556
     -0.07219808      -0.49010458       0.34403411
      0.63805046       0.03123465       0.46999929
      0.50838374       0.00754431       0.46372876
      0.20742016      -0.23715390       0.31145651
      0.21957350       0.63504600       0.31129793
      0.49252565       0.97213243       0.52739381
      0.46254946       0.86699495       0.51338367
      0.46833659       0.30083696       0.47570094
      0.56435815       0.28642228       0.46051829
      0.73586863      -0.12693724       0.63650708
      0.75181963      -0.25406949       0.63203814
      0.41854353       0.84406884       0.44927074
      0.33515626       0.90054023       0.46728072
      0.34479509       0.57962028       0.37911763
      0.29762780      -0.47903310       0.40660055
      0.15115248       0.54108257       0.49957979
      0.08260965       0.53074503       0.52635427
      0.89266849       0.40696421       0.52478091
     -0.06057907       0.40486920       0.55352216
      0.55977900      -0.37296647       0.61748251
      0.53858714      -0.26767121       0.59987163
      0.71275400       0.42250550       0.56832405
      0.78839559       0.34546846       0.58417890
      0.67385329      -0.19610180       0.44987464
      0.59318198      -0.16624091       0.42828513
      0.12312508       0.37123899       0.28937208
      0.05023666       0.27675971       0.29997236
     -0.16681739       1.58406768       0.63195176
     -0.21800579       1.57002107       0.66191007
      0.20675683      -0.06108281       0.29221359
      0.10312049      -0.09294129       0.30396903
      0.20277637       0.06067826       0.60416144
      0.19887396      -0.00744650       0.62890026
      0.42062864      -0.24439336       0.35497596
      0.36814211      -0.33879224       0.34193308
     -0.46114333       0.32802380       0.39548517
      0.45713828       0.41873416       0.39179412
      1.05751346       0.29067408       0.55923161
      1.04348507       0.18703047       0.57744764
      0.21179010       0.87249263       0.56793233
      0.09036024       0.85931851       0.57432053
      0.60751605       1.01609789       0.65259722
      0.72696147       1.05338974       0.65871807
      0.44683747       0.21956247       0.29940199
      0.48216169       0.19981749       0.26927194
      0.10930269       0.40445023       0.47082959
      0.17010928       0.50009382       0.45569496
      0.78757796      -0.20083679       0.40459572
      0.81784835      -0.20993279       0.37400609
      0.63044955      -0.50216422       0.32507910
      0.61823261      -0.56783464       0.29754461
      0.38298254       1.64224442       0.61713447
      0.27391580       1.65127025       0.62769264
     -0.18349257       0.40823838       0.42743175
     -0.11707568       0.32822140       0.44206697
      0.37713689       0.15324147       0.36153587
      0.47188832       0.15561964       0.38076476
      0.84313290       0.66869553       0.54540293
      0.78036268       0.55967659       0.53781156
      0.62834565       0.07729786       0.39976222
      0.58336683       0.13133194       0.42359675
      1.57461032       1.43827952       0.71246905
      1.47093630       1.44260924       0.69550961
      0.56330564       1.09120276       0.50193580
      0.61593811       1.12895503       0.52786251
      0.73348421       0.31660428       0.46194097
      0.75096480       0.20702765       0.47568711
      0.18544389      -0.23514793       0.40166768
      0.22931162      -0.14674533       0.42153910
      0.36292308       0.50876490       0.64987458
      0.33531338       0.38470088       0.66057777
      1.49747974      -0.54677440       0.44932443
      0.51766749      -0.42535318       0.46152212
      1.85759374       0.75185320       0.76879203
      0.88557936       0.66337125       0.74776712
      0.66151301       0.68965700       0.41313588
      0.60698800       0.57649179       0.41787791
     -0.21783861       0.90704975       0.72268493
     -0.18062377       1.02010056       0.73108294
      0.79398077       0.91221618       0.53177815
      0.89172292       0.88245064       0.51170593
      1.21360535       1.19956259       0.58314768
      1.23188220       0.10388812       0.56520461
      0.69217913      -0.02288592       0.35644459
      0.65013288      -0.02349422       0.32542268
      0.49314736       0.09990072       0.55428120
      0.40698133       0.13735440       0.57630192
      0.06940342       0.10352406       0.53021711
      0.12918295       0.01423295       0.54673459
      1.23761207       0.03882752       0.37085803
      0.23384130       0.05388881       0.33858930
     -0.50295222       0.92300366       0.74813821
     -0.38930037       0.97841032       0.74266531
      0.13655853       0.16157403       0.39040653
      0.15373516       0.09867462       0.41870070
      0.35793276       0.15462364       0.64561652
      0.44313351       0.08542197       0.66008140
      0.12490452       1.60323574       0.67914603
      0.10103912       0.67758518       0.66052594
     -0.02910081      -0.04303719       0.33290797
     -0.08397074      -0.06715582       0.30625602
      0.47100963      -0.31135459       0.42347049
      0.44678381      -0.21727665       0.40309666
      0.17380547       1.23522872       0.64351497
      0.28087835       1.29207879       0.63186950
      0.72243965       1.04679669       0.60136565
      0.77633776       1.15885707       0.60968516
      0.20332595       1.15182338       0.29172154
      0.31769260       1.09822536       0.28860721
      0.90406410       0.53849761       0.41088426
      0.78463589       0.58505950       0.41470974
      1.12942702       1.53845314       0.71988868
      1.20054880       1.43235266       0.71382259
     -0.17158886       0.30160650       0.40269399
     -0.07101085       0.26515881       0.38366272
      0.74322462       1.32613449       0.64589263
      0.77475704       1.41411198       0.62227898
      0.14620565      -1.10616729       0.48008239
      0.18160223      -0.03968360       0.50606301
     -0.11186987       0.94149530       0.65599853
     -0.13718975       1.02669042       0.63199678
      0.56159298       0.19900069       0.59311202
      0.55920469       0.18285975       0.62176711
      0.90336505       0.15667383       0.52548512
      0.98450787       0.25110265       0.52511525
      0.97847305      -0.42779836       0.72340892
      1.02887897       0.67051183       0.71108441
      0.93053153      -0.03352705       0.43016463
      0.94358325       0.08994529       0.42307038
     -0.12458051       0.56502080       0.45311411
     -0.04730932       0.59270705       0.47590220
     -0.26829199       0.80830572       0.49363371
     -0.21717255       0.70457633       0.48040899
      0.43110180       0.68638080       0.68890088
      0.32510025       0.62119216       0.70042335
      0.12431384       0.78282478       0.61843684
      0.20700484       0.81000752       0.64341301
      0.70384786       0.11901625       0.29636532
      0.58157041       0.12693352       0.30130944
      0.75363478       0.23168055       0.54459190
      0.75644483       0.12259613       0.56105372
     -0.03231861       0.12955620       0.32499376
     -0.09853097       0.23584383       0.32218754
      1.35833840      -0.44225252       0.44591484
      1.25776038      -0.35606860       0.43991425
      0.02974229      -0.01448169       0.38634402
     -0.04925278      -0.12297578       0.38637941
      0.07972722      -0.25141011       0.36219086
      0.18306699      -0.31067445       0.35551374
      0.92747522       0.76466556       0.60868816
      0.95937680       0.87571382       0.62123825
      0.52932163       0.57770897       0.50403614
      0.58437494       0.68163282       0.49342216
      0.32115740       0.82996586       0.67667456
      0.25755504       0.94154338       0.67730506
     -0.22810590       0.37614398       0.49430267
     -0.18576922       0.49671288       0.49149878
      0.65189321       0.70221781       0.55887514
      0.58469375       0.80139057       0.54950481
      0.45751382       1.14320451       0.73814919
      0.45757048       1.25211787       0.71984711
     -0.16073265       0.53318711       0.58413419
     -0.04460020       0.52255466       0.59636621
      1.23763588       0.27151415       0.53650362
      0.26869350       1.37267158       0.55194387
      1.56531541       1.75888578       0.65789015
      1.64170785       1.76839833       0.68268336
      1.17071819       0.30450968       0.36193986
      1.07205789       0.24647217       0.34988931
      0.66268682       0.39143410       0.35576888
      0.77470013       0.33753052       0.36083320
      0.48701966      -0.62651414       0.32289219
      0.45172427      -0.71444999       0.34206563
      0.89274414       0.87693241       0.57141470
      0.77760242       0.86753703       0.58449204
      1.22348599      -0.38621798       0.54275880
      1.26314524      -0.31955173       0.56641379
      0.93813763       1.18794820       0.71316474
      0.91809214       1.10192472       0.69334364
      0.61064405       0.92402610       0.60719628
      0.55192305       1.01039312       0.59021354
      0.96908959       0.73238970       0.67284455
      0.86559314       0.75071650       0.65769890
      1.05951362      -0.45354408       0.38093143
      1.05009801      -0.58200279       0.37590291
      0.76172957       0.49270651       0.70861525
      0.72438777       0.60310359       0.69947487
      0.43493202       1.01642204       0.62370834
      0.41157215       0.90717107       0.63919892
      1.28709531       1.22977646       0.71568664
      1.22240102       1.24760104       0.69023856
     -0.36929002       0.30112790       0.68799301
      0.73835598       1.24904006       0.69307962
      1.08438837       1.16887216       0.75281234
      1.10337181       1.25880709       0.73309939
      0.00881530       0.23511529       0.66153556
      0.01992074       0.10863332       0.65331960
     -0.18762204       1.76544824       0.69589571
     -0.22099427       0.73159748       0.72364889
      0.47402075       0.21823941       0.52156939
      0.39449064       0.32549396       0.52603852
      0.49229702       0.00642229       0.70437200
      0.49041094      -0.09636789       0.68559144
      0.31519106       1.45346432       0.61090090
      0.38603816       1.37161975       0.59824648
      0.15729732       1.50568246       0.63546369
      0.21559092       1.47629782       0.66066682
     -0.19454501       1.01393222       0.39591120
     -0.22080313       1.12719611       0.38222917
      1.06810038       0.81254123       0.53206673
      1.06352248       0.70747723       0.51307936
     -0.12638475      -0.55537021       0.26026243
     -0.05760421      -0.65321822       0.26577609
     -0.09042409       1.07196610       0.58294900
      0.02325129       1.03828409       0.59636367
      0.32063486       0.92608540       0.72659258
      0.35574911       0.80830229       0.72123409
      0.10412373       0.41841079       0.59896831
      0.14274925       0.51651990       0.58178437
     -0.19591148       0.07044928       0.45554844
     -0.19021572       0.03340561       0.48590483
      1.07785299       0.53236279       0.30851784
      1.17527108       0.48273981       0.32369409
     -0.05242302       0.21986278       0.47826685
      0.04602452       0.20858933       0.45856538
      0.40878055       0.29190606       0.42949757
      0.35385287       0.26786429       0.40109729
      0.91361281       1.37763527       0.70485166
      0.92601382       1.37974445       0.73573816
      0.49180218       0.49176486       0.55630311
      0.38888954       0.54455977       0.56839724
      0.74382564       0.28498135       0.31337726
      0.81303180       0.29929615       0.28888582
      0.23876821       1.20570242       0.44319221
      0.19992227       1.11701411       0.46333591
      0.59407806       1.36278641       0.60873199
      0.54524237       1.46654437       0.59522322
      2.02346307       1.41217476       0.66399254
      1.91147497       1.37915850       0.65989115
      0.09845777       0.03688460       0.69616599
      0.09766268      -0.08531166       0.69167377
      1.25808011       0.44420386       0.36149889
      1.31081579       0.38358222       0.33934553
      0.07353811       0.81613159       0.44176424
     -0.02019300       0.78679404       0.46293839
      0.38984424       0.83369934       0.56338610
      0.37381688       0.87922811       0.59234427
      0.51453372      -0.09541985       0.35009748
      0.39484305      -0.06645979       0.35017125
      0.55593924       0.38753163       0.51869390
      0.66004756       0.46315941       0.51627573
      0.64848801       0.61180544       0.37008072
      0.57832658       0.64084106       0.34599612
      0.75386845      -0.15146447       0.33086236
      0.73564205      -0.27427126       0.33331691
     -0.09648741       0.50938984       0.32488838
      0.56504329       0.06286545       0.46968741
      0.24293994       0.69761578       0.32091286
      0.48108748       0.89535134       0.53166188
      0.49757936       0.32553516       0.45789152
      0.76744020      -0.18340073       0.62487691
      0.41144876       0.90246316       0.46247378
      0.31794376      -0.48573743       0.38681989
      0.12877684       0.58271134       0.51624414
      0.95851509       0.39985886       0.53493477
      0.52243754      -0.30282985       0.61791897
      0.76895759       0.37346632       0.56560940
      0.66848522      -0.18560993       0.43043112
      0.09074693       0.30162769       0.28441615
     -0.20154125       1.61789646       0.64720226
      0.17181260      -0.12468412       0.29662573
      0.15700557       0.00871911       0.61363921
      0.42233976      -0.32994901       0.35514866
      0.53286785       0.40322511       0.39184579
      1.07727341       0.25676911       0.57497686
      0.13716955       0.87720865       0.55959520
      0.68216863       0.99627546       0.65137040
      0.45119708       0.16614064       0.28412456
      0.10973328       0.48171438       0.46781222
      0.84388934      -0.20664059       0.39174052
      0.58303852      -0.54048463       0.31286474
      0.32808472       1.59763404       0.62452336
     -0.19165309       0.33704380       0.43457786
      0.41823919       0.20183034       0.37245093
      0.78587144       0.61673307       0.55124293
      0.56011355       0.11309492       0.40567704
      1.51701295       1.39737040       0.70673631
      0.54695764       1.10711476       0.52102138
      0.72131688       0.27947218       0.47879616
      0.18444949      -0.21210987       0.42113103
      0.36668171       0.45488107       0.66482426
      0.49064798      -0.46503727       0.44561439
      0.82820218       0.69414688       0.75657380
      0.65847198       0.61537373       0.40712496
      0.76748450       0.96128069       0.73583267
      0.81730697       0.91059549       0.51275491
      1.27220645       1.14795719       0.57873009
      0.64741928      -0.05620926       0.34353694
      0.48391157       0.12047094       0.57316210
      0.14376608       0.06922992       0.53329165
      1.27850839       0.03499489       0.35317314
     -0.46354066       0.99485951       0.74685190
      0.12508520       0.09293059       0.39933758
      0.43296574       0.12732681       0.64290755
      0.09700574       1.67696831       0.67957377
     -0.02662689      -0.02348385       0.31412699
      0.44363826      -0.24009345       0.42143376
      0.25025628       1.24855748       0.64562073
      0.79823150       1.08209822       0.60445310
      0.24357641       1.08550799       0.29686686
      0.84487510       0.54791453       0.42274978
      1.20665739       1.51259035       0.71454551
     -0.14852600       0.27439958       0.38483199
      0.79875463       1.36570466       0.63635127
      0.20013661      -0.05770220       0.48695782
     -0.08803369       1.01243312       0.64786941
      0.60681036       0.21343304       0.60836199
      0.96760512       0.18267756       0.51744002
      1.01869709      -0.36164031       0.72861865
      0.89279549       0.03025280       0.42811891
     -0.12190623       0.58173239       0.47257350
     -0.28364610       0.74658147       0.48027041
      0.35461305       0.69479199       0.69387913
      0.17636099       0.75539076       0.63132326
      0.64567772       0.08234767       0.30555919
      0.74693252       0.15345949       0.54261621
     -0.02750156       0.20761939       0.32607759
      1.27987775      -0.43232854       0.43958099
      0.00284833      -0.07336365       0.37560644
      0.13403374      -0.30077764       0.37038742
      0.98462893       0.81761037       0.60965656
      0.51924082       0.63814697       0.49321682
      0.28461449       0.88126714       0.66475622
     -0.20914894       0.44302019       0.50652580
      0.58914466       0.74769132       0.56398020
      0.41471483       1.19061656       0.72530883
     -0.12231266       0.52176874       0.60092233
      0.26021422       1.34539425       0.53435665
      1.56662855       1.77066279       0.67736079
      1.10461724       0.26953014       0.36735832
      0.72369042       0.35764108       0.34663600
      0.43147580      -0.68083095       0.32528778
      0.81926513       0.85574301       0.56746752
      1.25134221      -0.39325035       0.56126973
      0.87947711       1.14636757       0.70571444
      0.62353030       0.97359658       0.59258366
      0.91315731       0.79159814       0.67046472
      1.00887481      -0.51613717       0.38007575
      0.71990656       0.52980508       0.69520722
      0.42715157       0.93815001       0.61949356
      1.22065693       1.25957506       0.70894987
      0.68302181       0.25679220       0.67873356
      1.04556333       1.22974551       0.74538666
      0.05950376       0.17484591       0.65818294
     -0.25231321       1.76973735       0.70816158
      0.45404841       0.29350534       0.51621152
      0.47580393      -0.01885257       0.68583286
      0.31607039       1.37827042       0.60641490
      0.13921945       1.47529964       0.65395905
     -0.24949740       1.04980313       0.38476573
      1.02198254       0.77527198       0.51809412
     -0.13269955      -0.63172943       0.26362895
     -0.01665243       1.05122555       0.57819040
      0.34830926       0.86183449       0.73481007
      0.08547124       0.49199314       0.59517301
     -0.22931968       0.07879046       0.47296684
      1.15374394       0.51400513       0.30712860
     -0.02575549       0.24426930       0.46122795
      0.33910288       0.28875076       0.42031444
      0.89222545       1.42242644       0.72114703
      0.45112644       0.49752204       0.57217511
      0.78732813       0.24777689       0.30076703
      0.17546728       1.17137686       0.45167807
      0.60114018       1.43939441       0.60809185
      1.96388141       1.37112395       0.67251971
      0.13553192      -0.02618932       0.70064801
      1.23640886       0.39518318       0.34779401
      0.01704024       0.84626979       0.45444055
      0.34009588       0.83637329       0.57759905
      0.44929940      -0.11284502       0.35947285
      0.58008850       0.46021347       0.52387715
      0.65101061       0.61092524       0.34954978
      0.79285789      -0.22059881       0.33571374

INCAR

The INCAR files are provided in each section separately.

KPOINTS

The KPOINTS file contains only the Gamma-point:

Gamma-point only
 0
Monkhorst Pack
 1 1 1
 0 0 0

POTCAR

Standard POTCAR files are used throughout:

  • PAW_PBE H 15Jun2001
  • PAW_PBE O 08Apr2002
  • PAW_PBE Fe_sv 23Jul2007

This is different to in Ref. , where GW POTCARs are used.

Step-by-step instructions

1. Preparing the MLFFs

First, train the MLFFs for the water slab (128H2O_slab) and the redox pairs ([math]\displaystyle{ [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_n]^{3+} }[/math] and [math]\displaystyle{ [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_n]^{2+} }[/math]).

2. Calculating the vacuum potential

Run a molecular dynamics (MD) simulation, then calculate the local potential [math]\displaystyle{ \phi }[/math] of the water slab. Using this, the difference between the Oxygen 1s level between the water slab and the water molecules far away from the ions in the redox cells can be calculated. This provides the chemical potential relative to the vacuum [math]\displaystyle{ e \Delta \bar{\phi} }[/math].

3. TI from oxidized to reduced state

Perform a thermodynamic integration from the oxidized state (λ=0; Fe3+) to the reduced state (λ=1; Fe2+).

4. TI from MLFF to GGA

Perform a thermodynamic integration from MLFF (λ=0) to RPBE+D3 (λ=0). This should be done separately for Fe3+ and Fe2+.

5. TPT from GGA to hybrid (not covered here)

Due to the high cost of converting from RPBE to PBE0, we omit describing thermodynamic perturbation theory (TPT):

  • From RPBE+D3 to PBE0 (Fe3+)
  • From RPBE+D3 to PBE0 (Fe2+)

6. Analysis

Once each step is completed, you will have the following values:

  • the chemical potential - [math]\displaystyle{ e \Delta \bar{\phi} }[/math]
  • the free energy difference from MLFF to MLFF
    • from Fe3+ to Fe2+ - [math]\displaystyle{ \Delta A_{ML} }[/math]
  • the free energy difference from MLFF to GGA
    • Reduced: Fe2+ - [math]\displaystyle{ \Delta A^{FP_{GGA}-ML}_1 }[/math]
    • Oxidized: Fe3+ - [math]\displaystyle{ \Delta A^{FP_{GGA}-ML}_0 }[/math]

Take a summation over these to obtain the free energy difference from Fe3+ to Fe2+ on the GGA level [math]\displaystyle{ \Delta A^{FP_{GGA}} }[/math]. Finally, add [math]\displaystyle{ \Delta A^{FP_{GGA}} }[/math] to the redox potential relative to the standard hydrogen electrode (SHE) [math]\displaystyle{ U^{FP_{GGA}}_{redox} }[/math] (4.44 eV [1]). In our testing the results matched the literature to within 30 meV.

Our results are summarized in the following table:

Step Term Ours (eV) Lit. (eV)
2 - Vacuum reference [math]\displaystyle{ e \Delta \bar{\phi} }[/math] -3.71 -3.74
3 - TI (MLFF) [math]\displaystyle{ \Delta A_{ML} }[/math] -4.98 -4.95
4 - TI (GGA) [math]\displaystyle{ \Delta A^{FP_{GGA}-ML}_1 - \Delta A^{FP_{GGA}-ML}_0 }[/math] -0.055 -0.049
Absolute redox potential [math]\displaystyle{ \Delta A^{FP_{GGA}} }[/math] -5.03 -5.00
Redox potenital [math]\displaystyle{ U^{FP_{GGA}}_{redox} }[/math] 0.59 0.56

Recommendations and advice

  • The calculated values can change depending on the POTCAR file used, e.g., the final [math]\displaystyle{ \Delta U^{FP_{GGA}}_{redox} }[/math] was 0.8 eV when using GW POTCARs.

Related tags and articles

How-tos
Theory
Tags

References