[Wannier] Constraint centers positions and disentanglement check point

[Nicola Marzari]

Dear Angelo,


for the combined system, are you using centers and projectors that
match as closely as possible the ones you found for the two separated
systems?

If the case, my only guess is that you might have used a disentanglement
window that is too small. Try to look at the separate and the combined
band structures, to get a sense what states you should be spanning.

In general, there shouldn't be a lot of chemistry or charge transfer 
going on in your system, so what you get in the spearated case should be
a very good starting point.

With regards to your questions, 1) is something that we should 
implement, sooner or later. Conceptually, it means minimizing the
expectation value of (r-rfixed)^2, i.e. <r^2> -2<r>rfixed - so
it's a matter of regrouping terms and updating the gradient.

Re 2), I do not think there is any runtime flag that one could
use, but (if not) maybe we should consider for the future having
the possibility of re-tuning on-the-fly the wannier parameters.


			nicola


On 03/10/2012 16:20, Angelo Ziletti wrote:
> Dear WannierUsers,
> I am using Wannier90 to get parameters for a tight-binding Hamiltonian.  My system consists of a polymer on top of a graphene sheet.
> I got the MLWFs for the graphene and the polymers (separated).
> I want to calculate the hopping integrals between the MLWFs of the polymer and the MLWFs of the graphene; so, I did the electronic structure with polymer and graphene together.
> I have lots of trouble to get the MLWF centers in meaningful positions (i.e. right symmetries)  and the right band structure interpolation.
>
> So, I have two questions:
> 1) how can I constraint the position of the Wannier Functions during the spread minimization procedure? (namely, I want to use the information from the separate calculations - the graphene-polymer interaction is weak)
> 2) how can I put a check-point in the disentanglement? (the disentanglement is taking very long)
>
> Thanks for your attention.
>
> Angelo Ziletti
> PhD Candidate - School of Physics
> University College Dublin
> angelo.ziletti at gmail.com
>
>
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-- 

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Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL