[Q-e-developers] smearing style

[Jiqiang Li]

Dear Stefano,
       The system is a semiconductor, but it is +1 charged. Pwscf forces me to set a value for degauss. I want to evaluate the <f|dVtot/dR|i>, where the |i> and |f> refer to the wavefunctions of valence band maximum (VBM) and the isolated state induced by defect in the band gap, respectively. I found that the related wavefucntions change a lot when the weights (occupations) of the highest bands change. By the way, I am performing a Gamma point only calculation for a large supercell with a lattice constant exceeding 10 Angstrom.
        I believe the many quantities (such as total energy) do not change significantly when the occupations of highest states vary, because contribution from these states is relatively small than that from the rest states. So I am wondering whether it is normal that wavefunctions of highest occupied states change remarkably when the occupations of highest states vary.

Best regards!
Jiqiang



 
From: stefano de gironcoli
Date: 2015-09-20 04:07
To: q-e-developers
Subject: Re: [Q-e-developers] smearing style
Dear Jiqianq
 the answer to your question depends on which physical quantity you want to calculate.
 Is the state you want to study spatially localized ? is it an isolated (narrow band) in a band energy gap ? are you interested in the shallow donor states formed by the holes at the bottom of the conduction band of a doped semiconductor ? Or is your system a metal ?
 clarifying to yourself what is the question you want to answer will help you to figure out how to compute a physically meaningful number. 

stefano

On 19/09/2015 12:37, Jiqiang Li wrote:
Dear Lorenzo,
        For example, for a supercell with 100 electrons, it will be of 99 electrons when the system is +1 charged. I consider the 50th band as the highest occupied band with half occupation.

Jiqiang



 
From: Lorenzo Paulatto
Date: 2015-09-19 18:14
To: General discussion list for Quantum ESPRESSO developers
Subject: Re: [Q-e-developers] smearing style
Dear Jiqiang,
the "highest occupied banda" are obviously defined only for insulators, i.e. 
there is no such thing as a highest occupied bands when using a smearing, what 
threshold do you use for occupied/non occupied? 
 
kind regards 
 
On Saturday, September 19, 2015 05:48:09 PM Jiqiang Li wrote:
> Dear developers,
>         I want to use the wavefunctions of highest occupied bands  in a
> charged system to evaluate some quantities, such as psi_i(r) ＊psi_j(r) .
> However, I found that the wavefunction sensitively depends on the degauss
> value.  So, how to choose a suitable value for  degauss when I want  to
> obatain a physically meaningful quantity.
> 
> Best regards!
>  Jiqiang Li
> 
> 
> 
 
-- 
Lorenzo Paulatto - Paris
 
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