[Pw_forum] Relaxation with Spin-Orbit Coupling

[Dal Corso Andrea]

Please provide the input. This should not happen.

Andrea




On Tue, 2010-07-13 at 11:07 +0200, Julen Ibanez Azpiroz wrote:
> Hello
> 
> I would like to make a question to anyone who has experience in using
> the spin-orbit coupling (SOC). My problem is as follows:
> 
> 
> I relax a structure WITHOUT including SOC by the method damped
> dynamics:
> 
> 
> /
> &IONS
>  ion_dynamics = "damp",
>  pot_extrapolation = "second_order",
>  wfc_extrapolation = "second_order",
> /
>  with the time interval dt=20, and I get a structure where the forces
> are <1.0D-4Ry/au. Lets call this structure A.
> 
> Now, I include the SOC, and I run an scf calculation with structure A.
> It turns out that there are quite big forces, of the order of
> 0.01Ry/au. The energy of the unit cell with structure A and SOC
> included is -207.10202515 Ry.
> 
> Then, I try to relax the forces with SOC included with the same method
> as before. It relaxes (forces<1.0D-4), but in a structure quite
> different form A; lets call this new structure B. The surprising thing
> is that now, in structure B, the energy is -207.08231311 Ry, higher
> than with structure A. To summarize:
> 
> Calculations with SOC included:
> 
>           Structure A->  -207.10202515 Ry, forces of the order of
> 0.01Ry/au
>           Structure B->  -207.08231311 Ry, forces <1.0D-4Ry/au
> 
> Besides, if I plot the energies of the different structures that go
> from A to B when relaxing with SOC included, I see that the energy
> increases in each step going from A to B, and the energy of A seems to
> be in the botttom of a parabola. So, everything suggests that
> structure A is the most stable structure even when SOC is included,
> except there exist forces. I have checked the convergence with respect
> to the cutoff and the k point mesh, and I have used the same
> parameters in the calculations without SOC and with SOC.
> 
> I do not know how the forces are calculated when SOC is included, and
> I do no know who to trust, the energy or the forces. I will apreciatte
> very much any help, thank you in advance
> 
> 
> Julen Ibañez Azpiroz
> 
> University of the Basque Country
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-- 
Andrea Dal Corso                    Tel. 0039-040-3787428
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