[Pw_forum] Status of NMR?

[Davide Ceresoli]

Konstantin Kudin wrote:
>  Dear Joe,
> 
>  I'll comment!
> 
>  At the risk of sounding politically unpopular :-), my suggestion is
> the following. While you are waiting for NMR in QE, use CPMD for NMR
> calculations. From what I have seen, it works quite well for that
> purpose, and parallelization is excellent.
> 
>  Kostya 

Dear Kostya,
     at the risk of sounding politically unpopular :-), with CPMD you
can compute only the relative $^1$H chemical shifts, since there is
no reconstruction whatsoever.

As shown in PRB 63, 24510, in a pseudopotential approach, the chemical
shift is made up of four terms: the core contribution, the bare term,
the paramagnetic correction and the diamagnetic correction.

- the bare term is the contibution from valence electrons.

- the core term can be computed from an atomic calculation and does
   not depend on the chemical environment.

- the diamagnetic correction depends slightly on the chemical
   environment.

- the paramagnetic correction depends a lot on the chemical
   environment.

If you are interested in the *relative* chemical shifts, only the
core contributions cancels out, while the paramagnetic and diamagnetic
do not! Hydrogen is a very particular case, since the paramagnetic
correction vanishes and the diamagnetic one is nearly constant.

This said, I would like to remember that Quantum-Espresso is a GPL, 
community based project, and everyone is welcome to contribute
as much one can. I'm not getting paid for this job and I'm working on 
other projects. There are still unsolved bugs in the PAW part.
If anyone would like to help...

The code has not disappeared in the CVS version. I guess the NMR_new
directory is not tagged for the download using the "anonymous" CVS.

Best regards,
     Davide

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   Davide Ceresoli <ceresoli at sissa.it>
   Scuola Internazionale Superiore di Studi Avanzati (SISSA)
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