[Wannier] Nonorthogonal wannier function

[Nicola Marzari]

Dear Claudio,

the current Wannier90 code deals only with orthogonal wavefunctions.

Non-orthogonal WFs have been recently used in linear-scaling
quantum Monte Carlo approaches - both Andrew Williamson (Williamson
and Reboredo) and Dario Alfe' have developed some heuristic approaches
based on projections (a maximal localization strategy on non-orthogonal
WFs is somehow ill-conditioned: if you take a rare gas atom, the 
orthogonal MLWFs are 4 sp3 hybrids, but the non-orthogonal MLWFs would
probably be 4 identical s orbitals, each with an infinitesimal amount
of sp3 thrown in, to preserve linear independence).

Paolo Umari has coded the Williamson (or Alfe') algorithm as part of his
GW work, in a Gamma sampling implementation only - so I'm CC'ing him.

The plan on our side is to insert by the summer the orthogonal
Gamma-specific routines of localization and disentanglement into the
Wannier code (these have been written by Manu Sharma and Young-Su Lee).

Having a non-orthogonal option would also be great - and if you were 
interested or involved, it would also be great to coordinate.

				nicola



Claudio Attaccalite wrote:
> Hi
> 
> a simple question:
> 
> 1) it is possible to obtain nonorthogonal wannier functions (ok if want 
> call them very localized orbitals) with the wannier code?
> 
> 2) if not, does someone know another code that does it? or you think it 
> is easy to modify the wannier code in such a way to relax the 
> orthogonality condition?
> 
> Thanks
> 
> Claudio
> 
> 
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> Claudio Attaccalite
> 
> Institute for Electronics, Microelectronics, and Nanotechnology
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Prof Nicola Marzari   Department of Materials Science and Engineering
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