[Pw_forum] question

[Stefano Baroni]

Hi! I would like first of all to congratutate Wang Yanchao on his  
digging into the code. This is a very good practice, which I would  
like to encourage.

If I may just add a comment to the already exhaustive answer of Andrea:

>> "0",then "(t_rev.eq.1)"is false .This indicate that Cu`structure has
>> no time revers. But in fact,  Cu`structure is fcc,it should have time
>> revers.

the same holds not only for fcc, but for ANY finite as well as  
infinite system in the absence of magnetic fields ...

cheers - Stefano B.

On Oct 25, 2006, at 2:00 PM, Andrea Dal Corso wrote:

> On Wed, 2006-10-25 at 19:44 +0800, wang yanchao wrote:
>> Dear all:
>>     I have a question  when  I read the source program of PWscf.The
>> route of the source program is PWscf/PW/kpoint_grid.f90.In it I find
>> "if(t_rev(ns).eq.1) xkr=-xkr".I think "t_rev" is used to decide time
>> revers.But  I write "t_rev" when I caculate example01 namely  Cu`s
>> scf.The result is "0"rather than "1".I feel very confused. if it is
>> "0",then "(t_rev.eq.1)"is false .This indicate that Cu`structure has
>> no time revers. But in fact,  Cu`structure is fcc,it should have time
>> revers.So I do not know it clearly.Could you please tell me why ? 
>> Thank
>> you!
>>
>>
>
> The reason is that t_rev is set and used only with magnetic spin-orbit
> calculations. In this case there might be symmetry operations which
> require multiplication by the time reversal operator.
> In all other cases t_rev is set to zero, but time reversal is
> implicitly used because the code takes only k or -k, not both.
>
> Andrea
>
>
>
>>
>>
>>
>> sincerly
>>
>> Yanchao Wang
> -- 
> Andrea Dal Corso                    Tel. 0039-040-3787428
> SISSA, Via Beirut 2/4               Fax. 0039-040-3787528
> 34014 Trieste (Italy)               e-mail: dalcorso at sissa.it
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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