[Pw_forum] About NMR calculations for metallic system.

[Davide Ceresoli]

Young Cheol Choi wrote:
> Thank you Mr. Ceresoli for your fast reply.
> I'm so sorry for not being able to calculate the NMR shift for metallic 
> system using PWSCF.
> 
> But, I found your paper (Int. J. Quant. Chem. 2009, 109, 3336.), 
> where you calculated the NMR shift for the metallic system like graphene 
> or graphite,
> and you didn't include the Knight shift.
> 
> 1) so, I thought that it is possible to calculate the NMR shift for 
> metallic systems using PWSCF,
>     though it is not considering the Knight shift. Am I right?
>     (cf. in the case of the Castep code where the same theory (GIPAW) is 
> implemented,
>     I could not perform such calculations for the system with fractional 
> occupation number
>     ,that is to say, metallic systems.)
>
> 2) If I'm right, is it meaningful to calculate the NMR shift for 
> metallic system without the Knight shift?
>     I'm asking this question cause, as far as I know, the Knight shift 
> is much larger than chemical shift.
Dear Choi,
    the Int. J. Quant. Chem. paper refers to the so-called
"converse" method (JCP 131, 101101). This is not yet available
in the CVS version and it's in the list of the 1000+1 things
I'm plannig to do. Anyway, we haven't implemented yet the Knight
shift, but it should be straightforward.

As you mention, in some systems the Knight shift is much larger
than the NMR shift, and it doesn't make sense to compute only
the latter. However, according to literature, for undoped
graphite or graphene, the Kinght shift is small.


> 3) lastly, Is it possible to calculate the NMR shift for the 
> paramagnetic system using PWSCF?
>     (maybe, spin-polarized calculations for the NMR shift.)
The GIPAW code (which does linear response), should work
also for spin polarized systems (magnetic insulators).
I've never tried though...

> Sorry for too many questions.
> And thank you very much, Mr. Ceresoli.
> 
> Best regards,
> Choi.
You are very welcome!

Best,
    Davide