[Pw_forum] Overlap integral for periodic part of eigenfunction

[Vahid Askarpour]

Dear Lorenzo,

Thank you so much for pointing out the pw2wannier90.x code. I have seen this code in the wannier90-2.0.1/pwscf/v5.0
folder and it only calculates the overlap for the nearest neighbor k-points (loops over nnb in the compute_mmn subroutine). The one you referred to does not have this limitation. I will give it a try.

Best wishes,

Vahid


> On Mar 16, 2017, at 5:14 AM, Lorenzo Paulatto <lorenzo.paulatto at impmc.upmc.fr> wrote:
> 
> On Wednesday, March 15, 2017 11:11:54 PM CET Vahid Askarpour wrote:
>> I would like to calculate the overlap integral  u*_k’(r)u_k(r)d^3r. 
> 
> Dear Vahid,
> if you want to do it for excercize, go on and do it.
> 
> But, you may be happy to know that this integral is already computed in 
> several places in the pw code. One in particular is the pw2wannier90.x code in 
> particular in  PP/src/pw2wannier90.f90 from line 2120 to line 2187
> 
> (and in general all the compute_mmn subroutine, but it does also a few more 
> operations and some parts related to ultrasoft pseudopotentials are a bit 
> difficult to understand)
> 
>> 1. Am I correct in assuming that the above integral is equivalent to the
>> sum(C*_k C_k’), where C’s are the coefficients from evc.dat and the sum is 
>> over igwx (maximum G-vector index) specified in eve.dat? 
> 
> No, i I remember correctly the wfcs on files are in G-space. Doing the product 
> in G-space is equivalent to doing a convolution in real space.
> 
>> 2. igwx is different for different k-points. One k-point may have igwx=1459
>> while another k-point has igwx=1468. In the above sum, is it correct to 
>> to use the top 1468 coefficients of the first k-point to calculate the overlap
>> integral between the two k-points?
> 
> No, because the order is not necessarily the same. Also, because you wouldn't 
> be doing the product of the two functions but their convolution.
> 
> hth
> 
> 
> -- 
> Dr. Lorenzo Paulatto 
> IdR @ IMPMC -- CNRS & Université Paris 6
> phone: +33 (0)1 442 79822 / skype: paulatz
> www:   http://www-int.impmc.upmc.fr/~paulatto/
> mail:  23-24/423 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
> 
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