[Pw_forum] how to consider the "dt" flag during vc-relax

Chaohao Hu chaohao.mse at gmail.com
Tue Oct 23 09:29:12 CEST 2007

Dear Cesar,

Thank you for your reply. According to your suggestion, I change "dt" and
conv_thr to 80 and 1.D-10, the convergence is not improved, although the
calculation is running.  The  calculated  total  force  and  stress  is
given here as a attachment because it is too long. As you can see from this
file, the final cell parameters is changed  largely, which also affects the
k-points meshing during my calculation. Another point added here is that my
systems only contain some light elements like H, Li. How to further optimize
these parameters?


On 10/23/07, Cesar R.S. da Silva <cesards at msi.umn.edu> wrote:
> Dear Chao,
> Your dt setting should work OK. wmass could be reduced to somthing like
> 0.002, provided atomic masses are all set to the average mass (amu), but
> your value is not that bad. The only thing I think could produce
> convergence problems is your conv_thr. Try conv_thr = 1e-9. Variable cell
> requires precise stress calculation, and a more stringent convergence
> criteria for the SCF cycle is required.
> Cesar.
C.H. Hu
Postdoctoral fellow
Chimie et Physico-Chimie appliquees
Institut Francais du Petrole (IFP)
Rueil-Malmaison, France
E_mail: chaohao.mse at gmail.com
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