[Pw_forum] how to treat free electron gas, especially how to setup input file

[Stefano Baroni]

Hem, what a weird request!
Why not doing the exercise with pencil-and-paper?
If you insist using a very sophisticated code to do that, you have two options, I believe, both of which will require somewhat more work than the simple pencil-and-paper exercise.
dig into the code where the the hamiltonian*wavefunctions operations are performed (the routine used to be called "h_psi", and simply have the the multiplication times the external potential skipped, which will set the electrons "free" ...
build a fake pseudo-potential which is simply null, and feed it into the computer ...
HTH - Stefano B


On Jan 3, 2012, at 6:42 PM, Jun Liu wrote:

> Dear All,
> 
> Let me wish all of you a Happy New Year first.
> 
> Maybe this is a very fundamental problem, but I cannot google any hint online, so here I am. I would like to work out a free electron gas problem with QE. I know total number of charges, and the size of the box the electrons move in and probably periodic b.c. applied to it. Now how can I possibly set up the input file for it? It seems many fundamentional properties of a lattice do not come with free electron gas. The code itself should be well-defined for a lattice system, so how is the code adapted to the free electron problem?
> 
> Thank you very much,
>  
> Sincerely,
> Jun Liu
> 
> 
> 
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget

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