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This is a follow-up question to my question posted here. I've been trying to study the effects of spin-orbit coupling (SOC) on the band structure of ferromagnetic (FM) material VSe$_{2}$. The input file for the SCF calculation using Quantum ESPRESSO (QE) is given below.

&CONTROL calculation = 'scf' outdir = './outdir' verbosity = 'high' tprnfor = .true. tstress = .true. pseudo_dir = '.' / &SYSTEM ibrav = 0 A = 3.35381 nat = 3 ntyp = 2 ecutwfc = 55 ecutrho = 650 starting_magnetization(1) = 1 starting_magnetization(2) = 0 lspinorb = .true. noncolin = .true. occupations = 'smearing' smearing = 'mv' degauss = 0.005d0 / &ELECTRONS conv_thr = 1e-8 mixing_beta = 0.7d0 / CELL_PARAMETERS {alat} 1.000000000000000 0.000000000000000 0.000000000000000 -0.500000000000000 0.866025403784439 0.000000000000000 0.000000000000000 0.000000000000000 2.087308375869810 ATOMIC_SPECIES V 50.94150 V.rel-pbe-spnl-kjpaw_psl.1.0.0.UPF Se 78.96000 Se.rel-pbe-dn-kjpaw_psl.1.0.0.UPF ATOMIC_POSITIONS {crystal} Se 0.666666666666667 0.333333333333333 0.774935000000000 Se 0.333333333333333 0.666666666666667 0.225065000000000 V 0.000000000000000 0.000000000000000 0.000000000000000 K_POINTS {automatic} 6 6 6 0 0 0

This did not converge when I consider the starting_magnetization of Vanadium to be 1 but converges when I assign a starting magnetization of 0 to Vanadium.

And I couldn't find any example of SOC being considered for Magnetic systems.

So is it necessary to start with a starting_magnetization of zero for magnetic systems while considering SOC?

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  • $\begingroup$ SOC has got nothing to do with the starting_magnetization tag. $\endgroup$ Commented Jan 29, 2021 at 21:37

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And I couldn't find any example of SOC being considered for Magnetic systems.

So is it necessary to start with a starting_magnetization of zero for magnetic systems while considering SOC?

  • In short, the answer is NO.

  • The magnetic materials usually are calculated with spin-polarized mode (collinear), in which the electrons are classified into spin-up and spin-down and you only assign the initial magnetic momentum for each atom (just a number).

  • However, for magnetic materials with heavy atoms, you should do the noncollinear magnetic calculations, in which you should open the tag of SOC and set the initial magnetic momentum for each atom (a $1 \times 3$ vector) at the same time.

  • You may take a look at the explanation about the initial magnetization in vaspwiki.

  • For QE, you could take a look at the following tutorial to do noncollinear magnetic calculations:

  • https://www.youtube.com/watch?v=AxfW1iSaz_U

  • May it helps.

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As a beginner and to the best of my knowledge

  1. spin-orbit coupling is irrelevant to the magnetic properties.
  2. Spin-orbit coupling is related to relativity which is increasingly important for heavier for elements around Krypton and onward, and also if you're aiming for high precision.
  3. For convergence, try to increase electron_maxstep >> 100 (maximum number of iterations in a scf step). and set conv_thr (Convergence threshold for selfconsistency) to the default value 1e-6.
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