[Pw_forum] time-reversal symmetry broken

[Stefano Baroni]

Timo: I do not have a solution handy, and others may have deeper  
ideas. I think the problem is that when simmetrizing the charge  
density the code always assumes e(k)=e(-k) and psi(-k)=psi(k)*, and  
so it never uses more than 1/2 the BZ. One thing you may try is to  
pass explicitly all the k-points, and wish that the code is not so  
smart as to remove 1/2 of them ... Otherwise, I do not see any other  
options than hacking the code (but, again, others may have smarter  
ideas). SB

On Nov 21, 2007, at 4:04 AM, Timo Thonhauser wrote:

> Dear All,
>
> I have a question concerning the breaking of time-reversal symmetry
> within PWscf. For my proposes I have modified the code and included a
> (periodic) vector potential into the Hamiltonian. The code gives very
> good results for the quantity that I am interested in for molecules,
> i.e. gamma-point calculations. However, when I try to do calculations
> for periodic solids, the results worsen.
>
> I think the code (unless you do spin-orbit coupling) assumes time-
> reversal symmetry. In principle, including a vector potential breaks
> time-reversal symmetry. But, in the cases of my gamma-point  
> calculations
> that did not cause any problems ( psi_(-k)=psi_(k)* for k=gamma ) and
> hence, I get good results for molecules. However, maybe this is the
> problem with my calculations for extended systems: including the
> vector potential breaks time-reversal symmetry, and
> in general psi_(-k) is not psi_(k)*, but the code is not "aware"
> that the symmetry has been broken.
>
> Thus, my question is: is there a simple way to tell the code that
> time-reversal symmetry is broken without getting into spin-orbit
> stuff?
>
> Thanks,
> Timo Thonhauser, MIT
>
> ______________________________________________________________________
>
> Dr. TIMO THONHAUSER
> Department of Materials Science and Engineering         (617) 253 6026
> MIT, 13-4084, 77 Massachusetts Avenue               thonhauser at mit.edu
> Cambridge, MA 02139-4307, USA                    www.mit.edu/~thonhaus
> ______________________________________________________________________
>
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
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