[molpro-user] OQVCCD does not converge at extreme geometries, but CCSD does

[Tibor Győri]

Yes, I have tried {oqvccd(t);shift,1,1} and
{oqvccd(t),shifts=0.2,shiftp=0.2,thrdis=1.0;diis,1,1,15,1;maxit,100;}
Since I only tried these at a single geometry, it is possible that they
would help at the other problematic geometries, but they are no silver
bullet.

2017-05-22 7:42 GMT+02:00 Peterson, Kirk <kipeters at wsu.edu>:

> Dear Tibor,
>
> so you tried shifting both the singles and pairs via something like:
>  {oqvccd(t);shift,1,1}   ?
>
> best,
>
> -Kirk
>
> > On May 21, 2017, at 5:54 AM, Tibor Győri <tiborgyri at gmail.com> wrote:
> >
> > Dear Molpro users,
> >
> > Recently I have run into some issues while trying to use OQVCCD(T) for
> the purpose of calculating energies for PES fitting. The problem is, that
> to fit a global PES some calculations have to be run at pretty extreme
> geometries, and I have seen many examples, where ordinary CCSD and CCSD-F12
> converges but OQVCCD does not.
> >
> > The awesome multiple bond breaking characteristics of OQVCCD(T) would be
> really advantageous for fitting a global PES, but these convergence issues
> are hindering my efforts. I have tried to increase the maximum number of
> iterations allowed to 100, but a number of calculations still do not
> converge.
> > I also tried to use level shifts and increased DIIS size at one
> geometry, but it did not work any better.
> >
> > Is there anything I could do to increase the chance of OQVCCD converging
> in difficult cases? Since these input files are automatically generated,
> anything that requires manual per-input tuning is pretty much out of the
> question.
> > I have attached an abridged log file of a calculation that had issues.
> >
> > Best wishes,
> > Tibor Győri
> > MSc student
> > University of Szeged
> >
> > <oqvccd.log>_______________________________________________
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> > Molpro-user at molpro.net
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