[Pw_forum] time-reversal symmetry broken

[Nicola Marzari]

Stefano Baroni wrote:
> 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

Timo - what about the no_sym flag ? I thought that that would allow
to force pwscf not to try to symmetrize the points (e.g. if
one wanted to use a Baldereschi point, such as 1/4 1/4 1/4) - since
it does not attempt to symmetrize anything, it might not use
time reversal (rambling hypothesis - I'm sure SdG or PG know better,
as always the case :-) ).

As a side note - once k and -k are treated separately, even
if the Hamiltonian is invariant for time reversal,
in principle it's not psi(-k)=psi(k)* , but you might
find more generally that psi(-k) = exp (i alpha) psi(k)* ,
where alpha is random.


			nicola


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