[Pw_forum] questions on molecular dynamics example

[Paolo Giannozzi]

On Dec 28, 2006, at 18:21 , Eduardo Ariel Menendez P wrote:

> I think that wfc_extrapolation acts only for the first self-consistent
> iteration at any ionic configuration [...]
> pot_extrapolation influences the guess for the potential, then it  
> has a
> direct influence on the number of iterations needed for self- 
> consistency.

in principle correct, but since the first diagonalization is often  
performed
with a rather large threshold, the output wavefunction will often have
enough "memory" of the input one to influence self-consistency
(according to Murphy's law, in a negative way). The ideal combination
would be extrapolation of the wavefunctions + extrapolation of the
potential + a wise choice of the diagonalization threshold; of course
if the ionic steps are small enough

Paolo
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Paolo Giannozzi, Democritos and University of Udine, Italy