I am running a calculation using Vasp 5.4.4 on a coincidence lattice system with a total of 182 ions. The system consists of Sb2Te3 and a TMDC compound. There are three different TMDC compounds in the study. All three systems were structurally relaxed (without spinorbit coupling) without problem. Similarly, I was able to calculate the band structure for each system without trouble (again without spinorbit coupling). For two of the systems, the SOC calculations converge without problem, but for the third (MoS2), the system fails to converge. There are a total of 182 atoms in the system consisting of 2 ML of MoS2 and 7 QL of Sb2Te3. The computational cell has a 1:10 aspect ratio with the zaxis being significantly longer.
I then took the relaxed structures and attempted to include the effects of spinorbit coupling. For two of the systems, the system converged fine while the third system did not. I have tried many variations of input and k points, but the system always has diverged in energy. This occurred even when ICHARG=12 (fix charges) was set. There are 1120 electrons in the system and enlarged the number of bands to 1500 to avoid numerical troubles. I have no idea what to try next hence my inquiry here.
N E dE d eps ncg rms rms(c)
DAV: 1 0.649191374646E+04 0.64919E+04 0.38243E+05 50816 0.106E+03
DAV: 2 0.100053666920E+03 0.65920E+04 0.62718E+04 57696 0.209E+02
DAV: 3 0.800304317535E+03 0.70025E+03 0.67965E+03 55920 0.740E+01
DAV: 4 0.829168447772E+03 0.28864E+02 0.28265E+02 59760 0.146E+01
DAV: 5 0.830553120111E+03 0.13847E+01 0.13781E+01 72432 0.314E+00 0.171E+01
DAV: 6 0.830390999775E+03 0.16212E+00 0.61298E01 65032 0.105E+00 0.103E+01
DAV: 7 0.830371226976E+03 0.19773E01 0.17680E01 57976 0.441E01 0.351E+00
DAV: 8 0.830367238150E+03 0.39888E02 0.56942E02 58064 0.335E01 0.114E+00
DAV: 9 0.298739524471E+04 0.21570E+04 0.23792E+02 57368 0.325E01 0.137E+01
DAV: 10 0.133848642162E+05 0.10397E+05 0.28436E+04 55488 0.279E+00 0.530E+01
DAV: 11 0.190743253401E+06 0.17736E+06 0.46255E+05 56256 0.343E+01 0.985E+01
DAV: 12 0.903883872139E+06 0.71314E+06 0.60175E+06 54964 0.431E+01 0.185E+02
DAV: 13 0.242854531447E+06 0.66103E+06 0.11228E+06 57220 0.102E+02 0.274E+02
DAV: 14 0.517376273239E+06 0.27452E+06 0.95459E+03 55588 0.295E+02 0.200E+02
DAV: 15 0.108644484194E+09 0.10813E+09 0.18256E+08 52828 0.457E+02 0.171E+02
DAV: 16 0.412246177950E+08 0.67420E+08 0.51783E+07 54864 0.589E+02 0.154E+02
DAV: 17 0.565707635239E+09 0.52448E+09 0.24748E+05 58112 0.605E+02 0.147E+02
DAV: 18 0.433209920258E+08 0.52239E+09 0.59808E+05 59696 0.710E+02 0.141E+02
A typical input file is attached below. Note that I have also tried ISMEAR = 1 (Gaussian smearing) and 5 (tetrahedron method with Blöchl corrections), increasing the kpoint density, both IBRION = 1 (quasiNewton) and 2 (conjugate gradient) and more. I am using a 4x4x1 Gamma centered mesh (the system is hexagonal) although I have increased the mesh density further only to encounter a similar divergence. I should also add that after the tutorial slide on convergence problems, I also set ICHARGE=12 (to fix the charge) only to find the SCF loop diverges like above. Note that the same system with Te and Se converges fine). Any suggestions as to what to try next would be gratefully received.
ALGO = Normal
EDIFF = 1E5
ENCUT = 420
IBRION = 2
ICHARG = 1
ISIF = 3
ISMEAR = 5
ISPIN = 2
ISYM = 1
LAECHG = True
LCHARG = True
LORBIT = 11
LREAL = False
LSORBIT = T
LVHAR = True
LWAVE = False
NELM = 100
NSW = 0
PREC = Accurate
SAXIS = 0 0 1
SIGMA = 0.05
NCORE = 9
AMIN = 0.01
NBANDS = 1500
SCF loop diverging with Spinorbit on
Moderators: Global Moderator, Moderator
 paulfons
 Newbie
 Posts: 15
 Joined: Sun Nov 04, 2012 2:40 am
 License Nr.: 51405
 Location: Tsukuba, Japan
 Contact:

 Administrator
 Posts: 2921
 Joined: Tue Aug 03, 2004 8:18 am
 License Nr.: 458
Re: SCF loop diverging with Spinorbit on
The solution to your problem is found in steps.
In the following description the vasp_ncl version was used in every step, even for collinear calculations, in order to have compatible WAVECARs.
If convergence problems appear for SOC/NCL calculations,
we usually try to obtain a solution without SOC/NCL at the Gamma point only and use this WAVECAR for the actual SOC/NCL calculation.
So following steps were done to obtain the solution for the full kpoint grid with SOC turned on in the noncollinear spin orientation.
1. Gammaonly calculation for LSORBIT = .FALSE. ; LNONCOLLINEAR = .FALSE. ; keep WAVECAR
2. use WAVECAR of previous step with LSORBIT = .FALSE. ; LNONCOLLINEAR = .TRUE. ; keep WAVECAR
3. use WAVECAR of previous step with LSORBIT = .TRUE. ; LNONCOLLINEAR = .TRUE. ; keep WAVECAR
4. Calculation with full kpoint grid (gammapoint must be included in grid) based on WAVECAR of previous step
Very often, step 2 can be skipped.
This does not apply to your system, but for magnetic systems in general the MAGMOM tag should be set in all steps to study the desired spinorientation.
This means, the user should set MAGMOM in step 1 (and 2) with LORBIT = 11, which results in an table of the form in the OUTCAR
The values in the last column can be used for MAGMOM in the INCAR for the noncollinear setup in step 3 and 4.
Note, however, that here 3 values for each ion should be supplied, as written on our wiki site:
https://cms.mpi.univie.ac.at/wiki/index ... NCOLLINEAR
In the following description the vasp_ncl version was used in every step, even for collinear calculations, in order to have compatible WAVECARs.
If convergence problems appear for SOC/NCL calculations,
we usually try to obtain a solution without SOC/NCL at the Gamma point only and use this WAVECAR for the actual SOC/NCL calculation.
So following steps were done to obtain the solution for the full kpoint grid with SOC turned on in the noncollinear spin orientation.
1. Gammaonly calculation for LSORBIT = .FALSE. ; LNONCOLLINEAR = .FALSE. ; keep WAVECAR
2. use WAVECAR of previous step with LSORBIT = .FALSE. ; LNONCOLLINEAR = .TRUE. ; keep WAVECAR
3. use WAVECAR of previous step with LSORBIT = .TRUE. ; LNONCOLLINEAR = .TRUE. ; keep WAVECAR
4. Calculation with full kpoint grid (gammapoint must be included in grid) based on WAVECAR of previous step
Very often, step 2 can be skipped.
This does not apply to your system, but for magnetic systems in general the MAGMOM tag should be set in all steps to study the desired spinorientation.
This means, the user should set MAGMOM in step 1 (and 2) with LORBIT = 11, which results in an table of the form in the OUTCAR
Code: Select all
magnetization (z)
# of ion s p d tot

1 0.000 0.000 0.000 0.000
2 0.000 0.000 0.000 3.753
3 0.000 0.000 0.000 0.406
4 0.000 0.000 0.000 0.000
Note, however, that here 3 values for each ion should be supplied, as written on our wiki site:
https://cms.mpi.univie.ac.at/wiki/index ... NCOLLINEAR