The ABINIT Users Mailing List ( CLOSED )

[Josef Zwanziger <jzwanzig@dal.ca>]

Dear Colleagues,
I've noticed this behavior in the past and never really understood it. I would
really appreciate an explanation from someone. 

When I optimize a cell with optcell = 1 or 2, and dilatmx = 1.1 and ecutsm /= 0
as required, I find typically that the cell optimizes nicely and the final
computed pressure is very small, of course determined by whatever value I set
tolmxf to. Then, if I cut and paste the new acell and xred and rprim, and do a
normal ground state SCF run with the same convergence level (using either
toldff or tolvrs), the computed final pressure is usually several orders of
magnitude larger than the final value achieved in the optimization run. For
example, if I choose really easy case like Si, I can optimize it to a computed
final pressure of 1E-4 GPa, and then those cell parameters in an SCF
calculation will give a pressure of 1E-2. This gets worse in big cells, where 
I
might optimize to 1E-2 and then the SCF run gives 1 GPa. Why does this happen?
It seems to be independent of the value of ecutsm, and also I am running at a
pretty dense kpt set (kptrlen = 80). Any comments?

thanks,
Joe Zwanziger