[Pw_forum] About NMR calculations for metallic system.

[Serguei Patchkovskii]

On Tue, 29 Sep 2009, Davide Ceresoli wrote:
> > 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...

Unlike NMR chemical shifts of closed-shell systems, chemical shift 
in paramagnetic species is a statistical (rather than a response) 
property. Generally speaking, you need to know all spin-Hamiltonian 
parameters to calculate it - the shielding tensor, the hyperfine tensor,
the g-tensor, and (if you radical sites are of a spin higher than
1/2) the zero-field splitting parameters. You may also need to know
the spin-spin and spin-lattice relaxation times, or at least have
an idea as to their magnitude relative to the NMR time scale.

You'll get a better idea of what's involved in such calculation
from our (by now slightly dated, but still basically OK) review:

S. Moon and S. Patchkovskii, "First-Principles Calculations of
Paramagnetic NMR Shifts", pp. 325-338, in M. Kaupp, M. Buehl, 
and V.G. Malkin (eds), "Calculation of NMR and EPR Parameters", 
Wiley-VCH, 2004.

For the simplest possible case (isolates spin-1/2 paramagnetic
centres, relaxing rapidly on the NMR time scale) you may be able
to get everything you need from GIPAW - but a fair bit of a bit 
of coaxing and head-scratching is likely to be involved ...

Have fun,

Serguei

---
Dr. Serguei Patchkovskii

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