### SCF loop diverging with Spin-orbit on

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**Mon Aug 20, 2018 8:40 am**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 spin-orbit coupling) without problem. Similarly, I was able to calculate the band structure for each system without trouble (again without spin-orbit 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 z-axis being significantly longer.

I then took the relaxed structures and attempted to include the effects of spin-orbit 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 -0.61298E-01 65032 0.105E+00 0.103E+01

DAV: 7 -0.830371226976E+03 0.19773E-01 -0.17680E-01 57976 0.441E-01 0.351E+00

DAV: 8 -0.830367238150E+03 0.39888E-02 -0.56942E-02 58064 0.335E-01 0.114E+00

DAV: 9 -0.298739524471E+04 -0.21570E+04 -0.23792E+02 57368 0.325E-01 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 BlĂ¶chl corrections), increasing the kpoint density, both IBRION = 1 (quasi-Newton) 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 = 1E-5

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

I then took the relaxed structures and attempted to include the effects of spin-orbit 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 -0.61298E-01 65032 0.105E+00 0.103E+01

DAV: 7 -0.830371226976E+03 0.19773E-01 -0.17680E-01 57976 0.441E-01 0.351E+00

DAV: 8 -0.830367238150E+03 0.39888E-02 -0.56942E-02 58064 0.335E-01 0.114E+00

DAV: 9 -0.298739524471E+04 -0.21570E+04 -0.23792E+02 57368 0.325E-01 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 BlĂ¶chl corrections), increasing the kpoint density, both IBRION = 1 (quasi-Newton) 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 = 1E-5

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