[Pw_forum] phonon calculations in a spercell of 100 atoms

Paolo Giannozzi giannozz at democritos.it
Mon Feb 13 21:45:09 CET 2012

On Feb 13, 2012, at 16:41 , Lorenzo Paulatto wrote:

> If you only need the phonons at  the gamma point, it may be faster
> to get them by finite displacement, doing 3*nat pw.x ground state  
> calculations.

faster? not sure, and not by much anyway. A phonon calculation at q=0  
requires 3*nat self-consistent linear-response calculations. Each  
such calculation
has a computational cost comparable to that of a self-consistency.  
Usually one
needs to perform two finite-difference calculations with opposite  
in order to get good numerical accuracy, by the way. Or at least,  
this is the way
I would do it.

For q=0 phonons, using k=0 only for the Brillouiin zone sampling, and  
PP, there is the simplified version of the phonon code that is  
definitely faster and takes
(relatively) little memory

Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

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