[Pw_forum] Silent Calculations

[S. K. S.]

On Sat, Aug 9, 2008 at 1:52 AM, Paolo Giannozzi <giannozz at democritos.it>wrote:
>  Only for Gamma point phonon  one  can use "Frozen
>  phonon" method because it is much faster.

not true in general. Each linear-response calculation
costs approx. as much as a self-consistent one, and
you need at least as many scf calculations as
linear-response calculations.

Dear Sir,
I agree with you that  for small system each
linear-response calculation
costs approx. as much as a self-consistent one, and
 we need at least as many scf calculations as
linear-response calculations.

However, IN CASE OF  very large system (say about 64 atoms per unit cell),
I found that  a single representation  takes too much computer time
compared to a single scf run.

Moreover, in some cluster which have multiple cpu
for each node and  in some quad or octa core  computer,  always
phonon paralization  is much slower than manual
scf paralization (I mean manually divide   your all  scf calculations in
different  processors).  In case of  Frozen phonon method, one can
also accomplish the same goal  by using less memory and
disk space.
However, for non-zone center phonon Linear response is the best way.
There is still a scope in PWSCF to make Phonon calculation much faster
by implementing the representation number parallization.

regards,
SKS
JNCASR
BANGALORE


On Sat, Aug 9, 2008 at 1:52 AM, Paolo Giannozzi <giannozz at democritos.it>wrote:

>
> On Aug 8, 2008, at 18:41 , S. K. S. wrote:
>
> >  Only for Gamma point phonon  one  can use "Frozen
> >  phonon" method because it is much faster.
>
> not true in general. Each linear-response calculation
> costs approx. as much as a self-consistent one, and
> you need at least as many scf calculations as
> linear-response calculations
>
> Paolo
> ---
> Paolo Giannozzi, Dept of Physics, University of Udine
> via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
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