[QE-users] Antw: Re: band structure with hybrid functional HSE

[Stefan Seidl]

Dear Lorenzo Paulatto,


thanks a lot for your message and the 4 possible ways how to calculate "band structure with hybrid functional eg HSE".
My answering took a while, because I wanted first to do the calculation you recommended me!

I choosed "Way 1":
- adding a k-point list with weight 0
- setting an extra q grid with the parameters  nqx1, nqx2, nqx3
  (it holds: nqx1 * n = kpoint1, with n is integer) 
 - setting: nosym =.true.,
                noinv=.true.


But something is disturbing. This is the error message from "CRASH":
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     task #        16
     from efermig : error #         1
     internal error, cannot bracket Ef
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Can you tell me please, why it is not working? I calculated a standard scf calculation for silicon! Preventive I added my input and output file in the appendix. Thanks a lot.

Best,
Stefan Seidl


>>> Lorenzo Paulatto <paulatz at gmail.com> 08.04.18 20.46 Uhr >>>
> Is there a workaround?

Hello,
The problem is quite fundamental, because in order to get the Fock 
operator at a certain k-point you need the wavefunctions on a grid that 
is commensurate with it, this can only be done self-consistently.

However, there are a few things you can do.

1. I think you can add k-points to the scf calculation with weight zero, 
this is boring (you'll have to specify he grid and the path by hand) and 
very computationally expensive.

2. you can interpolate the Fock operator, this should be possible if it 
is expressed om a basis of localized wavrfunctions. There is some 
development in this direction, but I don't know if it has been 
implemented already by someone.

3. You could interpolate the wavefunctions, from Wannier functions. This 
is probably impossible in practice.

4. You can interpolate the Hamiltonian, passing through a Wannier basis 
representation. This is possible, I have done it, and I've put an 
example in the git developement branch 
(PP/examples/W90_open_grid_example/). But you need to know, or learn, 
how to use Wannier90 (which is a useful skill regardless), and to use 
the developement version of qe.

kind regards

> 
> 
> Best,
> Stefan Seidl
> 
> 
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-- 
Lorenzo Paulatto - Paris
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