[Pw_forum] BFGS

[sbraccia carlo]

On Wednesday 12 May 2004 04:38 am, Silviu Zilberman wrote:
> Hi,
>
> Is there a way to feed an initial guess of the Hessian in the BFGS
> structural relaxation, instead of the (presumably) default unity matrix?
>
> Thanks, Silviu.

Yes, it is possible: whenever you start a new relaxation the code looks for a 
file prefix.hess and, if present, the inverse hessian written on that file is 
used as initial guess (an information message is also printed). If you can 
generate a good guess for the inverse hessian of your system you have only to 
write it on a file:

WRITE( unit, * ) SHAPE( inverse_hessian )
WRITE( unit, * ) inverse_hessian

where inverse_hessian is a 2-dim array. Put this file in the outdir and change 
the name to prefix.hess (prefix is the keyword set in &CONTROL).
Anyway, you can find all that you need in the file Modules/bfgs_mdule.f90, 
SUBROUTINES read_bfgs_file() and  terminate_bfgs().

carlo