[Pw_forum] Cell Relaxation

[Matthieu Fortin-Deschênes]

Dear Ali,

First, if you want to relax the cell, you need to use calculation='vc-relax'
Then you need to specify the namelist &cell, and also your namelist  
&ions is empty. As for what to put in those, you can look at the input  
file description:
http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm5993056
There are also examples on how to do this.

For your second question, the functional used is taken from the  
pseudopotential file and is specified in the file name of the  
pseudopotential. In your case you have pbe (gga). You can just change  
the pseudopotential to have another functional. I don't know anything  
about phonon calculations so I can't tell you what is more accurate.

What you get in the output file is cell parameters in alat units. That  
is in units of celldm(1). I don't think you can change it, but it only  
takes a few seconds to convert by yourself.

Also you should use a Gamma centered k-points mesh for hexagonal  
lattices and (6x6x1) seems too low to me. Did you check convergence  
wrt number of kpoints?

Matthieu Fortin-Deschênes
Polytechnique Montréal



ali.kamrani91 at yahoo.com a écrit :

> Dear users,
> First, I want to apologize for my very basic question. I am new to DFT.
> I know first step to do any kind of DFT calculations is to relax the  
> cell parameters. But unfortunately, I don't know how to do that. I  
> tried to run the attached input file but it does not seem to be  
> correct.
> My second question is what will differ if I want to relax my  
> structure using LDA or GGA? Is it just using  
> different pseudopotential files? Which approximation is more  
> accurate for phonon calculations?
> And my last question is, is it possible to obtain the relaxed cell  
> parameters based on angstrom?
> Thank you so much in advance.
> Kind Regards,
> Ali