[Wien] Spin-polarization VS no spin-polarization in GaN

[Peter Blaha]

What you did not show was that the minimization will give different 
forces too.

The minimization will stop once the forces are for a couple of times 
below 2.0 mRy (case.inM) and the movement is small enough.

Even very small differences between the sp and non-sp calculation will 
lead to a different minimization-path and thus mixer will stop by chance 
at different positions leading to different EFGs (and E-tot).

In other words: If you would really want to get out the same results in 
both runs you need to put the cut-off in case.inM very small, so that 
mixer will optimize the positions until the forces are really small in 
all cases.


On 04/08/2016 12:41 PM, Marcelo Barbosa wrote:
> Dear Sirs,
>
> I did some calculations with GaN (struct file in attachment) to compare the difference in energy and electric field gradient between the use of spin-polarization or not.
>
> The calculations were done using the commands
>
> init_lapw -b -ecut -8 -numk 480 -rkmax 7 (-sp)
> run(sp)_lapw -p -ec 0.00001 -cc 0.0001 -fc 0.5
>
> and the results were the following
>
> :ENE = -7995.60614872 (no spin-polarization)
> :ENE = -7995.60614871 (spin-polarization)
>
> :EFG001 = 0.57937 (no sp)
> :EFG001 = 0.57931 (sp)
>
> so they basically give the same.
>
> Then, I relaxed the structure using
>
> run(sp)_lapw -p -ec 0.00001 -cc 0.0001 -fc 0.5 -min
>
> and the results were
>
> :POS001 = 0.66667 0.33333 0.00002 (no sp)
> :POS001 = 0.66667 0.33333 0.00000 (sp)
>
> :POS002 = 0.66667 0.33333 0.37662 (no sp)
> :POS002 = 0.66667 0.33333 0.37701 (sp)
>
> :ENE = -7995.60615476 (no sp)
> :ENE = -7995.60615035 (sp)
>
> :EFG001 = 0.45038 (no sp)
> :EFG001 = 0.58801 (sp)
>
> so they gave different final positions and very different :EFG, as a consequence.
>
> However, if I use the final structure from the minimization without spin-polarization and do a calculation with spin-polarization (both from the beginning, using the previous commands), I get equal values
>
> :ENE = -7995.60615467 (no sp)
> :ENE = -7995.60615466 (sp)
>
> :EFG001 = 0.45036 (no sp)
> :EFG001 = 0.45034 (sp)
>
> and if I use the final structure from the minimization with spin-polarization and do a calculation without spin-polarization, I also get equal values
>
> :ENE = -7995.60614842 (no sp)
> :ENE = -7995.60614842 (sp)
>
> :EFG001 = 0.58272 (no sp)
> :EFG001 = 0.58271 (sp)
>
>
> This means that the only thing that I am getting different between them is the atomic positions during the minimization, since I always get the same :ENE and :EFG if both calculations are done with the same struct file.
>
> Is there any reason for this to happen?
> Which values for :ENE, :EFG and :POS should I consider the best, the spin-polarized ones or the ones without spin-polarization?
>
> Best regards,
> Marcelo
>
>
>
>
>
>
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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