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Since the effect of spin-orbit coupling plays an important role in a topological insulator, How to change the spin-orbit coupling strength in VASP?

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  • $\begingroup$ Welcome to our community! $\endgroup$
    – Jack
    Apr 5, 2021 at 8:04

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How to change the spin-orbit coupling strength in VASP?

Firstly, one can't realize this just by changing the input parameters in the INCAR for VASP. To tune the strength of spin-orbit coupling in VASP, you need to modify the source file vasp_source_code_path/src/relativistic.F and recompile it. For example, if you want to reduce the strength to half you can just multiply 0.5d0 to the $L \cdot S$ term in line 129 of relativistic.F:

       DO I=0,1
       DO J=0,1
       DO M =1,2*LL+1
       DO MP=1,2*LL+1
          DLLMM(LMP+MP-1,LM+M-1,J+2*I+1)=DLLMM(LMP+MP-1,LM+M-1,J+2*I+1)+ &
          0.5d0*SUM*LS(M,MP,I+2*J+1,LL)   !!!line 129 relativistic.F file
       END DO
       END DO
       END DO
       END DO

Note that you need to use the recompiled $vasp_ncl$ to run your calculation. As a benchmark, if you multiply 0.0d0 to the $L \cdot S$ term in line 129 of relativistic.F then you will receive the same result as the result obtained with vasp_std.

PS1: The answer is for the vasp.5.4.4.

PS2: You may take a look at this paper about the implementation of spin-orbit coupling in VASP. Or you may take a look at this post in matter modeling: Regarding spin-orbit coupling on DFT codes.

Hope it helps.

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  • $\begingroup$ Thacks for your answer. I will try to check it. $\endgroup$
    – LeiWang
    Apr 5, 2021 at 9:02
  • $\begingroup$ Is this legal? I mean, from the physical point of view... $\endgroup$
    – Camps ♦
    Apr 5, 2021 at 11:50
  • $\begingroup$ @Camps Mathematically meaningful. The SOC effect of real materials is hardly changed. Maybe you can only replace the atoms to realize that. $\endgroup$
    – Jack
    Apr 5, 2021 at 11:58
  • $\begingroup$ My concern is that, using that hack, you can fake the results. $\endgroup$
    – Camps ♦
    Apr 5, 2021 at 12:11
  • $\begingroup$ @Camps I guess the method is generally adopted just to investigate the gradual behavior of SOC. $\endgroup$
    – Jack
    Apr 5, 2021 at 12:17

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