[Pw_forum] relaxation

[Jess Kondor]

Hi, everyone,

 I have a question. Sometimes (at least, I found several times in the papers
for ferroelectrics), we need to relax a system with very tight criteria for
forces - up to 1 meV/Ang ( ~4.0d-5 in `pw (a.u.)` units). However, I found
that it is hard to achieve this criteria. If I use 'bfgs' with   conv_thr =
1.d-6 (or better) and upscale = 10.d0 , calculations often crashes with
message ''bfgs history was reset on the previous step...' and number of bfgs
steps = 15, number of scf steps = 2 . If I switch a relaxation method to
'damp' with dt=70.0, after one (or two) ionic steps forces are small, but
then 'Total force' increases rapidly (from 0.001 to 0.4 or something) and
remains almost constant. So, are there any other parameters which can help
in geometry relaxation?

cheers,
   Jess
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