VASP Forum

Dear VASP developers,

I am trying to perform an ionic relaxation on a 216-atom SQS supercell generated using ATAT. The system is a transition-metal oxide, where one transition-metal species is treated using DFT+U. The supercell is required to model a substitutional dopant concentration of 8.33%, which cannot be represented in the primitive cell. Therefore, I have not attempted relaxation of the primitive cell.
The calculation fails during the electronic SCF of the first ionic step and repeatedly produces the following error:

DAV: 66 -0.162254636541E+08 -0.13384E+08 -0.30348E+07 45312 0.127E+03
BRMIX: very serious problems
the old and the new charge density differ
old charge density: 1016.10899 new 1082.85917
0.297E+03

DAV: 67 -0.618439635378E+07 0.10041E+08 -0.36107E+07 59024 0.149E+03
BRMIX: very serious problems
the old and the new charge density differ
old charge density: 1082.85917 new 1054.74188
0.353E+03

DAV: 68 -0.472028896200E+07 0.14641E+07 -0.10767E+06 47648 0.136E+03
BRMIX: very serious problems
the old and the new charge density differ
old charge density: 1054.74188 new 1041.23457
0.331E+03

My INCAR is:

Global Parameters
ISTART = 0
ISPIN = 2
ICHARG = 2
LREAL = .FALSE.
ENCUT = 520
PREC = Accurate
LWAVE = .TRUE.
LCHARG = .TRUE.
ADDGRID= .TRUE.
LASPH = .TRUE.
MAGMOM = 12*0 24*5 12*0 24*0 144*0
GGA = PE
ISYM = 0

Static Calculation
ISMEAR = 0
SIGMA = 0.05
NELM = 300
EDIFF = 1E-05

AMIX = 0.2
BMIX = 0.0001
AMIX_MAG = 0.8
BMIX_MAG = 0.0001
MAXMIX = 80

NSW = 300
IBRION = 2
ISIF = 2
EDIFFG = -2E-02
POTIM = 0.3

NCORE = 6

DFT+U Calculation
LDAU = .TRUE.
LDAUTYPE= 2
LDAUL = -1 2 -1 -1 -1
LDAUU = 0 4.3 0 0 0
LDAUJ = 0 0 0 0 0
LMAXMIX = 4

I have already tried the following without success:

• ISYM = 0 and ISYM = -1

• ALGO = Fast, Normal, and VeryFast

• different AMIX, BMIX, AMIX_MAG, and BMIX_MAG values

• loser EDIFF and EDIFFG

• lower ENCUT

The electronic SCF never converges, so the ionic relaxation does not proceed. Could anyone suggest possible causes for this behavior or recommend additional settings that may improve convergence?

Dear tasdiquearman,

With the information you supply I can not help you. Please upload POSCAR, INCAR, KPOINTS and OUTCAR file.

All the Best Jonathan

Dear Jonathan,
I have uploaded the said files. I hope it helps!

Regards
Tasdique

Dear tasdiquearman,

Regarding the electronic optimization, set ALGO=all. This algorithm is known to be more robust for the kind of system you are dealing with.
If this does not work, try reducing the step size of the optimization algorithm with the tag TIME while still using ALGO=all.

I hope this is of help to you, otherwise feel free to come back to me.

All the Best Jonathan