Choosing pseudopotentials

Several pseudopotential variants labeled by suffixes exist for many elements. When making a choice, it is necessary to balance computational cost, accuracy, and transferability.

• To set up a minimal working example of your calculation, follow prepare a POTCAR.
• Try to create a smaller test calculation and perform your own tests to confirm if the quantity of interest is sensitive to the choice of the pseudopotential. It might be possible to opt for a computationally cheaper POTCAR and gain performance. On the other hand, it could be necessary to opt for a computationally demanding setup to obtain correct results.
• With the aspects described in the next section in mind, carefully look over the recommendations for each group in the periodic table.

Aspects to refine the choice of pseudopotentials

Aspect 1: Analyze the geometry of your structure for short bonds and the valency of the ions.

Short bonds will require harder potentials, and semicore states might have to be treated as valence for certain chemical bonding. For some elements, variants for specific valency exist; for example, the suffix _2 or _3 can be used to describe fixed divalent or trivalent Lanthanides.

Aspect 2: Consider the physical or chemical property that is the objective of your calculation.

If you are only interested in a rough structure optimization, soft potentials (_s) with minimal valency may suffice. This approach might also work for phonon calculations that rely on large supercells.

On the other hand, when optimizing a magnetic structure, it may be necessary to include semicore states in the valence (_pv and _sv).

For the computation of optical properties, it is crucial to use GW potentials.

Aspect 3: Scrutinize the requirements of the method or algorithm used in your calculation.

For any calculation involving unoccupied states significantly above the Fermi energy, the _GW variants of potentials are superior and should be used. Particularly, all kinds of calculations within many-body perturbation theory need a high number of empty bands. Therefore, when GW, BSE, etc. is performed, the GW potentials should be used throughout the workflow.

Hartree-Fock and hybrid caluclations should not be performed with soft potentials (_s). Moreover, any calculations where you switch the exchange-correlation functional should not be performed with soft potentials (_s).

For standard DFT-ground-state calculations, using _GW or _h potentials is usually unnecessary unless, e.g., the property of interest or geometry of the structure demands it.

Recommendations and advice

Recommended PAW potentials

The table directly below highlights recommended PAW potentials in bold.

These potentials are not ideal for calculations involving a large number of excited states as needed, e.g., for optical properties or many-body perturbation theory.

Standard PBE potentials (potpaw.64)
Potential name	Number of valence electrons	Valence electron configuration	ENAMX [eV]
H	1	1s1	250.0
H.25	0.25	1s0.25	250.0
H.33	0.33	1s0.33	250.0
H.42	0.42	1s0.42	250.0
H.5	0.5	1s0.5	250.0
H.58	0.58	1s0.58	250.0
H.66	0.66	1s0.66	250.0
H.75	0.75	1s0.75	250.0
H1.25	1.25	1s1.25	250.0
H1.33	1.33	1s1.33	250.0
H1.5	1.5	1s1.5	250.0
H1.66	1.66	1s1.66	250.0
H1.75	1.75	1s1.75	250.0
H_AE	1	1s1	1000.0
H_h	1	1s1	700.0
H_s	1	1s1	200.0
He	2	1s2	478.896
He_AE	2	1s2	2135.871
Li	1	2s1	140.0
Li_sv	3	1s2 2s1	499.034
Be	2	2s1.99 2p0.01	247.543
Be_sv	4	1s2 2s1.99 2p0.01	308.768
B	3	2s2 2p1	318.614
B_h	3	2s2 2p1	700.0
B_s	3	2s2 2p1	269.245
C	4	2s2 2p2	400.0
C_h	4	2s2 2p2	741.689
C_s	4	2s2 2p2	273.911
N	5	2s2 2p3	400.0
N_h	5	2s2 2p3	755.582
N_s	5	2s2 2p3	279.692
O	6	2s2 2p4	400.0
O_h	6	2s2 2p4	765.519
O_s	6	2s2 2p4	282.853
F	7	2s2 2p5	400.0
F_h	7	2s2 2p5	772.626
F_s	7	2s2 2p5	289.837
Ne	8	2s2 2p6	343.606
Na	1	3s1	101.968
Na_pv	7	2p6 3s1	259.561
Na_sv	9	2s2 2p6 3s1	645.64
Mg	2	3s2	200.0
Mg_pv	8	2p6 3s2	403.929
Mg_sv	10	2s2 2p6 3s2	495.223
Al	3	3s2 3p1	240.3
Si	4	3s2 3p2	245.345
P	5	3s2 3p3	255.04
P_h	5	3s2 3p3	390.202
S	6	3s2 3p4	258.689
S_h	6	3s2 3p4	402.436
Cl	7	3s2 3p5	262.472
Cl_h	7	3s2 3p5	409.136
Ar	8	3s2 3p6	266.408
K_pv	7	3p6 4s1	116.731
K_sv	9	3s2 3p6 4s1	259.264
Ca_pv	8	3p6 4s2	119.559
Ca_sv	10	3s2 3p6 4s2	266.622
Sc	3	3d2 4s1	154.763
Sc_sv	11	3s2 3p6 3d2 4s1	222.66
Ti	4	3d3 4s1	178.33
Ti_pv	10	3p6 3d3 4s1	222.335
Ti_sv	12	3s2 3p6 3d3 4s1	274.61
V	5	3d4 4s1	192.543
V_pv	11	3p6 3d4 4s1	263.673
V_sv	13	3s2 3p6 3d4 4s1	263.673
Cr	6	3d5 4s1	227.08
Cr_pv	12	3p6 3d5 4s1	265.681
Cr_sv	14	3s2 3p6 3d5 4s1	395.471
Mn	7	3d6 4s1	269.864
Mn_pv	13	3p6 3d6 4s1	269.864
Mn_sv	15	3s2 3p6 3d6 4s1	387.187
Fe	8	3d7 4s1	267.882
Fe_pv	14	3p6 3d7 4s1	293.238
Fe_sv	16	3s2 3p6 3d7 4s1	390.558
Co	9	3d8 4s1	267.968
Co_pv	15	3p6 3d8 4s1	271.042
Co_sv	17	3s2 3p6 3d8 4s1	390.362
Ni	10	3d9 4s1	269.532
Ni_pv	16	3p6 3d9 4s1	367.986
Cu	11	3d10 4s1	295.446
Cu_pv	17	3p6 3d10 4s1	368.648
Zn	12	3d10 4s2	276.723
Ga	3	4s2 4p1	134.678
Ga_d	13	3d10 4s2 4p1	282.691
Ga_h	13	3d10 4s2 4p1	404.601
Ge	4	4s2 4p2	173.807
Ge_d	14	3d10 4s2 4p2	310.294
Ge_h	14	3d10 4s2 4p2	410.425
As	5	4s2 4p3	208.702
As_d	15	3d10 4s2 4p3	288.651
Se	6	4s2 4p4	211.555
Br	7	4s2 4p5	216.285
Kr	8	4s2 4p6	185.331
Rb_pv	7	4p6 4d0.001 5s0.999	121.882
Rb_sv	9	4s2 4p6 4d0.001 5s0.999	220.112
Sr_sv	10	4s2 4p6 4d0.001 5s1.999	229.353
Y_sv	11	4s2 4p6 4d2 5s1	202.626
Zr_sv	12	4s2 4p6 4d3 5s1	229.898
Nb_pv	11	4p6 4d4 5s1	208.608
Nb_sv	13	4s2 4p6 4d4 5s1	293.235
Mo	6	4d5 5s1	224.584
Mo_pv	12	4p6 4d5 5s1	224.584
Mo_sv	14	4s2 4p6 4d5 5s1	242.676
Tc	7	4d6 5s1	228.694
Tc_pv	13	4p6 4d6 5s1	263.523
Tc_sv	15	4s2 4p6 4d6 5s1	318.703
Ru	8	4d7 5s1	213.271
Ru_pv	14	4p6 4d7 5s1	240.049
Ru_sv	16	4s2 4p6 4d7 5s1	318.855
Rh	9	4d8 5s1	228.996
Rh_pv	15	4p6 4d8 5s1	247.408
Pd	10	4d9 5s1	250.925
Pd_pv	16	4p6 4d9 5s1	250.925
Ag	11	4d10 5s1	249.844
Ag_pv	17	4p6 4d10 5s1	297.865
Cd	12	4d10 5s2	274.336
In	3	5s2 5p1	95.934
In_d	13	4d10 5s2 5p1	239.211
Sn	4	5s2 5p2	103.236
Sn_d	14	4d10 5s2 5p2	241.083
Sb	5	5s2 5p3	172.069
Te	6	5s2 5p4	174.982
I	7	5s2 5p5	175.647
Xe	8	5s2 5p6	153.118
Cs_sv	9	5s2 5p6 6s1	220.318
Ba_sv	10	5s2 5p6 5d0.01 6s1.99	187.181
La	11	4f0.0001 5s2 5p6 5d0.9999 6s2	219.292
La_s	9	5p6 5d1 6s2	136.53
Ce	12	4f1 5s2 5p6 5d1 6s2	273.042
Ce_3	11	5s2 5p6 5d1 6s2	176.506
Ce_h	12	4f1 5s2 5p6 5d1 6s2	299.9
Pr	13	4f2.5 5s2 5p6 5d0.5 6s2	337.25
Pr_3	11	5s2 5p6 5d1 6s2	181.719
Pr_h	13	4f2.5 5s2 5p6 5d0.5 6s2	400.742
Nd	14	4f3.5 5s2 5p6 5d0.5 6s2	338.34
Nd_3	11	5s2 5p6 5d1 6s2	182.619
Nd_h	14	4f3.5 5s2 5p6 5d0.5 6s2	402.016
Pm	15	4f4.5 5s2 5p6 5d0.5 6s2	340.358
Pm_3	11	5s2 5p6 5d1 6s2	176.959
Pm_h	15	4f4.5 5s2 5p6 5d0.5 6s2	404.406
Sm	16	4f5.5 5s2 5p6 5d0.5 6s2	341.177
Sm_3	11	5s2 5p6 5d1 6s2	177.087
Sm_h	16	4f5.5 5s2 5p6 5d0.5 6s2	405.382
Eu	17	4f6.5 5s2 5p6 5d0.5 6s2	344.705
Eu_2	8	5p6 6s2	99.328
Eu_3	9	5p6 5d1 6s2	129.057
Eu_h	17	4f6.5 5s2 5p6 5d0.5 6s2	403.212
Gd	18	4f7.5 5s2 5p6 5d0.5 6s2	342.859
Gd_3	9	5p6 5d1 6s2	154.332
Gd_h	18	4f7.5 5s2 5p6 5d0.5 6s2	407.403
Tb	19	4f8.5 5s2 5p6 5d0.5 6s2	340.855
Tb_3	9	5p6 5d1 6s2	155.613
Tb_h	19	4f8.5 5s2 5p6 5d0.5 6s2	405.043
Dy	20	4f9.5 5s2 5p6 5d0.5 6s2	341.547
Dy_3	9	5p6 5d1 6s2	155.713
Dy_h	20	4f9.5 5s2 5p6 5d0.5 6s2	405.886
Ho	21	4f10.5 5s2 5p6 5d0.5 6s2	343.845
Ho_3	9	5p6 5d1 6s2	154.137
Ho_h	21	4f10.5 5s2 5p6 5d0.5 6s2	415.91
Er	22	4f11.5 5s2 5p6 5d0.5 6s2	346.295
Er_2	8	5p6 6s2	119.75
Er_3	9	5p6 5d1 6s2	155.037
Er_h	22	4f11.5 5s2 5p6 5d0.5 6s2	429.583
Tm	23	4f12.5 5s2 5p6 5d0.5 6s2	344.206
Tm_3	9	5p6 5d1 6s2	149.221
Tm_h	23	4f12.5 5s2 5p6 5d0.5 6s2	419.812
Yb	24	4f13.5 5s2 5p6 5d0.5 6s2	344.312
Yb_2	8	5p6 6s2	112.578
Yb_3	9	5p6 5d1 6s2	188.359
Yb_h	24	4f13.5 5s2 5p6 5d0.5 6s2	409.285
Lu	25	4f14 5s2 5p6 5d1 6s2	255.695
Lu_3	9	5p6 5d1 6s2	154.992
Hf	4	5d3 6s1	220.334
Hf_pv	10	5p6 5d3 6s1	220.334
Hf_sv	12	5s2 5p6 5d4	237.444
Ta	5	5d4 6s1	223.667
Ta_pv	11	5p6 5d4 6s1	223.667
W	6	5d5 6s1	223.057
W_sv	14	5s2 5p6 5d5 6s1	223.057
Re	7	5d6 6s1	226.216
Re_pv	13	5p6 5d6 6s1	226.216
Os	8	5d7 6s1	228.022
Os_pv	14	5p6 5d7 6s1	228.022
Ir	9	5d8 6s1	210.864
Pt	10	5d9 6s1	230.283
Pt_pv	16	5p6 5d9 6s1	294.607
Au	11	5d10 6s1	229.943
Hg	12	5d10 6s2	233.204
Tl	3	6s2 6p1	90.14
Tl_d	13	5d10 6s2 6p1	237.053
Pb	4	6s2 6p2	97.973
Pb_d	14	5d10 6s2 6p2	237.835
Bi	5	6s2 6p3	105.037
Bi_d	15	5d10 6s2 6p3	242.839
Po	6	6s2 6p4	159.707
Po_d	16	5d10 6s2 6p4	264.565
At	7	6s2 6p5	161.43
Rn	8	6s2 6p6	151.497
Fr_sv	9	6s2 6p6 7s1	214.54
Ra_sv	10	6s2 6p6 7s2	237.367
Ac	11	6s2 6p6 6d1 7s2	172.351
Th	12	5f1 6s2 6p6 6d1 7s2	247.306
Th_s	10	5f1 6p6 6d1 7s2	169.363
Pa	13	5f1 6s2 6p6 6d2 7s2	252.193
Pa_s	11	5f1 6p6 6d2 7s2	193.466
U	14	5f2 6s2 6p6 6d2 7s2	252.502
U_s	14	5f2 6s2 6p6 6d2 7s2	209.23
Np	15	5f3 6s2 6p6 6d2 7s2	254.26
Np_s	15	5f3 6s2 6p6 6d2 7s2	207.713
Pu	16	5f4 6s2 6p6 6d2 7s2	254.353
Pu_s	16	5f4 6s2 6p6 6d2 7s2	207.83
Am	17	5f5 6s2 6p6 6d2 7s2	255.875
Cm	18	5f6 6s2 6p6 6d2 7s2	257.953
Cf	20	5f8 6s2 6p6 6d2 7s2	414.614

The following table highlights recommended PAW potentials for calculations involving many states above the Fermi energy in bold.

These potentials are not necessarily superior (and even might be inferior) for calculations involving mostly occupied states, e.g., for structural relaxations or phonons. They are optimized for scattering properties high above the Fermi level and thus have advantages if many unoccupied states are involved, as for optical properties or many-body perturbation theory.

GW potentials (potpaw.64)
Potential name	Number of valence electrons	Valence electron configuration	ENAMX [eV]
H_GW	1	1s1	300.0
H_GW_new	1	1s1	536.615
H_h_GW	1	1s1	700.0
He_GW	2	1s2	405.78
Li_AE_GW	3	1s2 2p1	433.699
Li_GW	1	2s1	112.104
Li_sv_GW	3	1s2 2p1	433.699
Be_GW	2	2s1.9999 2p0.001	247.543
Be_sv_GW	4	1s2 2p2	537.454
B_GW	3	2s2 2p1	318.614
B_GW_new	3	2s2 2p1	318.614
B_h_GW	3	2s2 2p1	731.373
C_GW	4	2s2 2p2	413.992
C_GW_new	4	2s2 2p2	433.983
C_h_GW	4	2s2 2p2	741.689
C_s_GW	4	2s2 2p2	304.843
N_GW	5	2s2 2p3	420.902
N_GW_new	5	2s2 2p3	452.633
N_h_GW	5	2s2 2p3	755.582
N_s_GW	5	2s2 2p3	312.986
O_GW	6	2s2 2p4	414.635
O_GW_new	6	2s2 2p4	466.797
O_h_GW	6	2s2 2p4	765.519
O_s_GW	6	2s2 2p4	334.664
F_GW	7	2s2 2p5	487.698
F_GW_new	7	2s2 2p5	480.281
F_h_GW	7	2s2 2p5	848.626
Ne_GW	8	2s2 2p6	432.275
Ne_s_GW	8	2s2 2p6	318.26
Na_sv_GW	9	2s2 2p6 3p1	372.853
Mg_GW	2	3s2	126.143
Mg_pv_GW	8	2p6 3s2	403.929
Mg_sv_GW	10	2s2 2p6 3d2	429.893
Al_GW	3	3s2 3p1	240.3
Al_sv_GW	11	2s2 2p6 3s2 3p1	411.109
Si_GW	4	3s2 3p2	245.345
Si_sv_GW	12	2s2 2p6 3s2 3p2	547.578
P_GW	5	3s2 3p3	255.04
S_GW	6	3s2 3p4	258.689
Cl_GW	7	3s2 3p5	262.472
Ar_GW	8	3s2 3p6	290.599
K_sv_GW	9	3s2 3p6 3d1	248.998
Ca_sv_GW	10	3s2 3p6 3d2	281.43
Sc_sv_GW	11	3s2 3p6 3d3	378.961
Ti_sv_GW	12	3s2 3p6 3d4	383.774
V_sv_GW	13	3s2 3p6 3d5	382.321
Cr_sv_GW	14	3s2 3p6 3d6	384.932
Mn_GW	7	3d6 4s1	278.466
Mn_sv_GW	15	3s2 3p6 3d7	384.627
Fe_GW	8	3d7 4s1	321.007
Fe_sv_GW	16	3s2 3p6 3d8	387.837
Co_GW	9	3d8 4s1	323.4
Co_sv_GW	17	3s2 3p6 3d9	387.491
Ni_GW	10	3d9 4s1	357.323
Ni_sv_GW	18	3s2 3p6 3d10	389.645
Cu_GW	11	3d10 4s1	417.039
Cu_sv_GW	19	3s2 3p6 3d10 4s1	467.331
Zn_GW	12	3d10 4s2	328.191
Zn_sv_GW	20	3s2 3p6 3d10 4s2	401.665
Ga_GW	3	4s2 4p1	134.678
Ga_d_GW	13	3d10 4s2 4p1	404.602
Ga_sv_GW	21	3s2 3p6 3d10 4s2 4p1	404.602
Ge_GW	4	4s2 4p2	173.807
Ge_d_GW	14	3d10 4s2 4p2	375.434
Ge_sv_GW	22	3s2 3p6 3d10 4s2 4p2	410.425
As_GW	5	4s2 4p3	208.702
As_sv_GW	23	3s2 3p6 3d10 4s2 4p3	415.313
Se_GW	6	4s2 4p4	211.555
Se_sv_GW	24	3s2 3p6 3d10 4s2 4p4	469.344
Br_GW	7	4s2 4p5	216.285
Br_sv_GW	25	3s2 3p6 3d10 4s2 4p5	475.692
Kr_GW	8	4s2 4p6	252.232
Rb_sv_GW	9	4s2 4p6 4d1	221.197
Sr_sv_GW	10	4s2 4p6 4d2	224.817
Y_sv_GW	11	4s2 4p6 4d3	339.758
Zr_sv_GW	12	4s2 4p6 4d4	346.364
Nb_sv_GW	13	4s2 4p6 4d5	353.872
Mo_sv_GW	14	4s2 4p6 4d6	344.914
Tc_sv_GW	15	4s2 4p6 4d7	351.044
Ru_sv_GW	16	4s2 4p6 4d8	348.106
Rh_GW	9	4d8 5s1	247.408
Rh_sv_GW	17	4s2 4p6 4d9	351.206
Pd_GW	10	4d9 5s1	250.925
Pd_sv_GW	18	4s2 4p6 4d10	356.093
Ag_GW	11	4d10 5s1	249.844
Ag_sv_GW	19	4s2 4p6 4d11	354.43
Cd_GW	12	4d10 5s2	254.045
Cd_sv_GW	20	4s2 4p6 4d10 5s2	361.806
In_d_GW	13	4d10 5s2 5p1	278.624
In_sv_GW	21	4s2 4p6 4d10 5s2 5p1	366.771
Sn_d_GW	14	4d10 5s2 5p2	260.066
Sn_sv_GW	22	4s2 4p6 4d10 5s2 5p2	368.778
Sb_GW	5	5s2 5p3	172.069
Sb_d_GW	15	4d10 5s2 5p3	263.1
Sb_sv_GW	23	4s2 4p6 4d10 5s2 5p3	372.491
Te_GW	6	5s2 5p4	174.982
Te_sv_GW	24	4s2 4p6 4d10 5s2 5p4	376.618
I_GW	7	5s2 5p5	175.647
I_sv_GW	25	4s2 4p6 4d10 5s2 5p5	381.674
Xe_GW	8	5s2 5p6	179.547
Xe_sv_GW	26	4s2 4p6 4d10 5s2 5p6	400.476
Cs_sv_GW	9	5s2 5p6 5d1	198.101
Ba_sv_GW	10	5s2 5p6 5d1 6s1	267.02
La_GW	11	4f0.2 5s2 5p6 5d0.8 6s2	313.688
Ce_GW	12	4f1 5s2 5p6 5d1 6s2	304.625
Hf_sv_GW	12	5s2 5p6 5d4	309.037
Ta_sv_GW	13	5s2 5p6 5d5	286.008
W_sv_GW	14	5s2 5p6 5d6	317.132
Re_sv_GW	15	5s2 5p6 5d7	317.012
Os_sv_GW	16	5s2 5p6 5d8	319.773
Ir_sv_GW	17	5s2 5p6 5d9	319.843
Pt_GW	10	5d9 6s1	248.716
Pt_sv_GW	18	5s2 5p6 5d10	323.669
Au_GW	11	5d10 6s1	248.344
Au_sv_GW	19	5s2 5p6 5d11	306.658
Hg_sv_GW	20	5s2 5p6 5d10 6s2	312.028
Tl_d_GW	15	5s2 5d10 6s2 6p1	237.053
Tl_sv_GW	21	5s2 5p6 5d10 6s2 6p1	316.583
Pb_d_GW	16	5s2 5d10 6s2 6p2	237.809
Pb_sv_GW	22	5s2 5p6 5d10 6s2 6p2	317.193
Bi_GW	5	6s2 6p3	146.53
Bi_d_GW	17	5s2 5d10 6s2 6p3	261.876
Bi_sv_GW	23	5s2 5p6 5d10 6s2 6p3	323.513
Po_d_GW	18	5s2 5d10 6s2 6p4	267.847
Po_sv_GW	24	5s2 5p6 5d10 6s2 6p4	326.618
At_d_GW	17	5d10 6s2 6p5	266.251
At_sv_GW	25	5s2 5p6 5d10 6s2 6p5	328.529
Rn_d_GW	18	5d10 6s2 6p6	267.347
Rn_sv_GW	26	5s2 5p6 5d10 6s2 6p6	329.758

Selecting a pseudopotential set

Generally, we recommend using the latest release of pseudopotentials.

Tip: For compatibility reasons or to accurately reproduce another calculation, you might need to use another (older) pseudopotential release. Consult the list of available pseudopotentials.

Hydrogen-like atoms with fractional valence

Twelve hydrogen-like potentials are supplied for a valency between 0.25 and 1.75. Further potentials might become available, c.f. available pseudopotentials. These are useful, e.g., to passivate dangling surface bonds.

Mind: The POTCAR files restrict the number of digits for the valency (typically 2, at most 3 digits). Therefor, using three H.33 potentials does yield 0.99 electrons and not 1.00 electron. This can cause undesirable hole- or electron-like states. Set the NELECT tag in the INCAR file to correct the total number of electrons.

First-row elements

For the 1st row elements B, C, N, O, and F, three potential versions exist, the plain one, a hard version, and a soft version. For most purposes, the standard version of PAW potentials is most appropriate. They yield reliable results for energy cutoffs between 325 and 400 eV, where 370-400 eV are required to predict vibrational properties accurately. Binding geometries and energy differences are already well reproduced at 325 eV. The typical bond-length errors for first row dimers (N₂, CO, O₂) are about 1% compared to more accurate DFT calculations. The hard pseudopotentials _h give results that are essentially identical to the best DFT calculations presently available (FLAPW, or Gaussian with very large basis sets). The soft potentials are optimized to work around 250-280 eV. They yield reliable description for most oxides, such as V_xO_y, TiO₂, CeO₂, but fail to describe some structural details in zeolites, i.e., cell parameters, and volume.

For Hartree-Fock (HF) and hybrid-functional calculations, we strictly recommend using the standard, standard GW, or hard potentials. For instance, the O_s potential can cause unacceptably large errors even in transition metal oxides. Generally, the soft potentials are less transferable from one exchange-correlation functional to another and often fail when the exact exchange needs to be calculated.

Tip: If dimers with short bonds are present in the system (H2O, O2, CO, N2, F2, P2, S2, Cl2), we recommend using the _h potentials. Specifically, C_h, O_h, N_h, F_h, P_h, S_h, Cl_h, or their _GW counterparts. Otherwise, the standard version is often the best choice for first-row elements.

Alkali and alkali-earth elements (simple metals)

For Li (and Be), a standard potential and a potential that treats the 1s shell as valence states are available (Li_sv, Be_sv). One should use the _sv potentials for many applications since their transferability is much higher than the standard potentials.

For the other alkali and alkali-earth elements, the semi-core s and p states should be treated as valence states as well. For lighter elements (Na-Ca), it is usually sufficient to treat the 2p and 3p states as valence states (_pv), respectively. For Rb-Sr, the 4s, 4p, and 5s, 5p states, must be treated as valence states (_sv).

Tip: For alkali and alkali-earth metals, the _sv variants should be chosen, other than for very light elements Na, Mg, K, and Ca, where _pv is usually sufficient.

p-elements

For Ga, Ge, In, Sn, Tl-At, the lower-lying d states should be treated as valence states (_d potential). For these elements, alternative potentials that treat the d states as core states are also available but should be used with great care.

d-elements

For the d elements, applies the same as for the alkali and earth-alkali metals: the semi-core p states and possibly the semi-core s states should be treated as valence states. In most cases, however, reliable results can be obtained even if the semi-core states are kept frozen.

When to switch from X_pv potentials to the X potentials depends on the required accuracy and the row for the 3d elements, even the Ti, V, and Cr potentials give reasonable results but should be used with uttermost care. 4d elements are the most problematic, and we advise using the X_pv potentials up to Tc_pv. For 5d elements the 5p states are rather strongly localized (below 3 Ry), since the 4f shell becomes filled. One can use the standard potentials starting from Hf, but we recommend performing test calculations. For some elements, X_sv potentials are available (,e.g., Nb_sv, Mo_sv, Hf_sv). These potentials usually have very similar energy cutoffs as the _pv potentials and can also be used. For HF-type and hybrid-functional calculations, we strongly recommend using the _sv and _pv potentials whenever possible.

Tip: As a rule of thumb the p states should be treated as valence states for d-elements, if their eigenenergy $\epsilon$ lies above 3 Ry.

f-elements

Due to self-interaction errors, f electrons are not handled well by the presently available density functionals. In particular, partially filled f states are often incorrectly described. For instance, all f states are pinned at the Fermi-level, leading to large overbinding for Pr-Eu and Tb-Yb. The errors are largest at quarter and three-quarter filling, e.g., Gd is handled reasonably well since 7 electrons occupy the majority f shell. These errors are DFT and not VASP related.

Particularly problematic is the description of the transition from an itinerant (band-like) behavior observed at the beginning of each period to localized states towards the end of the period. For the 4f elements, this transition occurs already in La and Ce, whereas the transition sets in for Pu and Am for the 5f elements. A routine way to cope with the inabilities of present DFT functionals to describe the localized 4f electrons is to place the 4f electrons in the core. Such potentials are available and described below; however, they are expected to fail to describe magnetic properties arising f orbitals. Furthermore, PAW potentials in which the f states are treated as valence states are available, but these potentials are expected to fail to describe electronic properties when f electrons are localized. In this case, one might treat electronic correlation effects more carefully, e.g., by employing hybrid functionals or introducing on-site Coulomb interaction.

For some elements, soft versions (_s) are available as well. The semi-core p states are always treated as valence states, whereas the semi-core s states are treated as valence states only in the standard potentials. For most applications (oxides, sulfides), the standard version should be used since the soft versions might result in s ghost-states close to the Fermi-level (,e.g., Ce_s in ceria). The soft versions are, however, expected to be sufficiently accurate for calculations on intermetallic compounds.

Lanthanides with fixed valence

In addition, special GGA potentials are supplied for Ce-Lu, in which f electrons are kept frozen in the core, which is an attempt to treat the localized nature of f electrons. The number of f electrons in the core equals the total number of valence electrons minus the formal valency. For instance, according to the periodic table, Sm has a total of 8 valence electrons, i.e., 6 f electrons and 2 s electrons. In most compounds, Sm adopts a valency of 3; hence 5 f electrons are placed in the core when the pseudopotential is generated. The corresponding potential can be found in the directory Sm_3. The formal valency n is indicted by _n, where n is either 3 or 2. Ce_3 is, for instance, a Ce potential for trivalent Ce (for tetravalent Ce, the standard potential should be used).

Warning: f-elements are notoriously hard to describe with DFT due to self-interaction errors in the strongly localized orbitals. Placing some, or all, 4f electrons in the core can rectify this issue, but then the description of magnetism will fail and transferability will suffer.

Tip: If you are not interested in 4f-magnetism, and know the valency of your lanthanide, use the _2 or _3 potentials.

Test your setup

Even if you have taken a lot of care to optimize your pseudopotential choice, it is always good to perform some test calculations with other potentials, if necessary on a small prototype system. You might realize that you need extra accuracy, or that you are leaving performance on the table by using unnecessarily hard POTCARs for your problem.

Related tags and sections

POTCAR, Prepare a POTCAR, Available pseudopotentials

Theoretical background: Pseudopotentials, Theory: Pseudopotential basics, Projector-augmented-wave formalism