[molpro-user] Mixed derivatives in Numerical Hessian
Werner Győrffy
gyorffy at theochem.uni-stuttgart.de
Sat Feb 11 11:06:37 CET 2017
Hi Benj,
Not to the best of my knowledge. Until now I have dealt with
implementing only gradients for closed-shell systems. However, toward
that end, a PhD student in our group is currently working on the
implementation of open-shell LMP2 analytical gradients.
Regards,
Werner.
On 02/10/2017 08:18 PM, Benj FitzPatrick wrote:
> Werner,
> Addressing the edge of curiosity, will open-shell CCSD/CCSD(T) also be
> getting analytic gradients?
> Thanks,
> Benj FitzPatrick
>
> On Tue, Feb 7, 2017 at 5:24 PM, Werner Győrffy
> <gyorffy at theochem.uni-stuttgart.de
> <mailto:gyorffy at theochem.uni-stuttgart.de>> wrote:
>
> Dear Aleksandr,
>
> I agree that the thresholds must be made tighter: especially for
> Hartree-Fock, and also for CP-HF in the case of using analytical
> gradients. One should be careful not to set the thresholds too
> tight. For example, the suggested "gthresh,orbital=1.0d-10" is
> equivalent to "{hf;accu,20;}" which seems to be unnecessary low and
> might cause convergence problems.
>
> Yes, MP2 and DF-MP2 Hessians are computed by using analytical first
> derivatives.
>
> CCSD(T) analytical gradients have been already implemented in the
> development version of Molpro. It will be hopefully available soon
> in the next release.
>
> Regards,
>
> Werner.
>
> On 02/06/2017 07:14 PM, sjk wrote:
>
> I find that tightening the convergence criterion on various
> evaluations
> generally solves the low frequency hessian convergence problems (my
> experience is that anything below about 200 cm-1 should not be
> considered reliable with the standard parameters).
> Thus, I generally insert the following line at the top of my
> input file
> gthresh,energy=1.0d-10, orbital=1.0d-10, oneint=1.0d-16,
> twoint=1.0d-16,
> optgrad=1.0d-6, compress=1.0d-13
> Best Regards,
> Stephen
> On Feb 6, 2017, at 9:12 AM, Leonid Shirkov
> <leonid.shirkov at gmail.com <mailto:leonid.shirkov at gmail.com>
> <mailto:leonid.shirkov at gmail.com
> <mailto:leonid.shirkov at gmail.com>>> wrote:
>
> Dear Colleagues,
>
> in some specific cases, the current accuracy of the
> numerical hessians
> is not enough, e.g. for very low frequency torsional
> vibrations (~50cm-1).
> The CCSD(T) freq analysis gives imaginary values instead of
> the real ones
> for the lowest modes. The solution is to find manually the
> hessian in
> the internal coordinates
> and then find the eigenvalues of the GF matrix, but that is
> a lot of work.
>
> If MP2 is used for such cases, then there are no imaginary
> frequencies.
> Do I understand correctly, that for MP2 freq analysis the
> hessians are
> found
> by differentiating the analytical MP2 gradients?
>
> Using the analytical gradients for highly accurate methods like
> CCSD(T) would probably resolve the problem,
> but they are not currently available in Molpro.
>
> Best regards,
> Leonid
>
> On Mon, Feb 6, 2017 at 10:18 AM, Werner Győrffy
> <gyorffy at theochem.uni-stuttgart.de
> <mailto:gyorffy at theochem.uni-stuttgart.de>
> <mailto:gyorffy at theochem.uni-stuttgart.de
> <mailto:gyorffy at theochem.uni-stuttgart.de>>> wrote:
>
> Dear Aleksandr,
>
> Numerical Hessians in Molpro are computed by using
> central finite
> differences with a 2-point formula as a default. That is
> a "general
> formula". That gives accurate results in most of the
> cases. There is a
> trade-off between accuracy and efficiency: More accurate
> finite field
> calculations would increase the number of single point
> calculations
> significantly. If one needs more accurate Hessians, it
> can be done
> only by
> computing that manually by using procedures.
>
> Regards,
>
> Werner.
>
>
> On 02/04/2017 02:04 AM, Aleksandr Lykhin wrote:
>
>
> Does anybody know how Molpro calculates mixed
> derivatives using central
> differences? It seems like it generates only two
> mixed displacements
> instead of four, so the general formula cannot be
> applied directly.
>
> --
> Kind regards, Aleksandr O. Lykhin.
>
>
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