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[TORRENT Marc <marc.torrent@cea.fr>]

Hi PMA and Joe,

Additional comment:

* ecutsm directly influence the way some plane waves are taken into account; so it has to be the same in both runs.
* dilatmx does not : it is only used to dimensioned arrays (in order to take into account future increasing of number of PW). And additional components are filled withs zeros.

In others words, internal variables are:
- ecut used to select plane-waves
- ecuteff=ecut*dilatmx**2 used to dimensioned arrays
Array components due to use of dilatmx and not included by ecut are filled with zeros.

But this is theory !; if a bug is there...

So Joe, aditional questions:
- is the total (converged) energy the same in both runs
- same question for forces...

If yes (for both questions) the problem probably occurs in 'forstrnps' routine where dilatmx might not be correctly taken into accound; but, this is speculation...

You also can test (as PMA asked) with and with the same dilatmx in the second run. It will give a good clue.
But the test proposed by PMA is not correct (sorry Pierre-Matthieu); using ecut*dilatmx**2 will necessarily give different results.

Marc



Anglade Pierre-Matthieu a écrit :

c65e87810810121221w7867ed2dx627000f7bd5940f4@mail.gmail.com" type="cite">

Hi,

You mentioned keeping ecutsm constant between the two runs but what
about dilatmx ?
Did you tried the second run with a ecut2=ecut1*dilatmx**2 ?

regards

PMA

On Sat, Oct 11, 2008 at 5:56 PM, Josef Zwanziger <jzwanzig@dal.ca> wrote:
  

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