[molpro-user] making start command valid in optg

[Phillip Peters]

Dear Gabriel and others,

Having now attempted to change the value of idir to other numbers I 
still have the same problem. The issue arises because of the varying 
step length taken depending on the curvature. When the gradient is at 
its largest value molpro takes a larger step. This should ofcourse 
correspond to a large change in the energy and thus correspondingly a 
large change in the CAS. As a consequence of the fact that it takes the 
previous points orbitals as an initial guess, which are no longer 
suitable, it fails to converge the CAS within the maximum number of 
iterations (set to 40 the maximum molpro allows for a single CAS). 
Changing idir to other values increased the number of steps taken before 
arriving at the problem region but it does not solve the problem as the 
change between the two regions is still to large.

Regards

Phillip



On 22/11/2011 15:30, Gabriel Freitas wrote:
> Dear Valérie and other collegues,
>
> I would also appreciatte the modification in the code regarding the 
> freedom in choosing guesses for IRCs / geometry optimzations / 
> frequencies calculations.
>
> Regarding the IRC step, you can choose it with the DIRECTION option in 
> optg directive. In addition to choosing the values +1 / -1 for 
> positive and negative directions, you can choose +n / -n (n natural), 
> which exactly determines the step lenght.
>
> I had also a similar problem with some convergence problems with ROHF 
> / CCSD(T) IRCs, and I found out that it had a crossing of states near 
> the problematic point. Although CAS can sometimes change smoothly 
> between sates, but not always. So I think it's worthy to check the 
> proximity of excited states near these points (with SA-CAS)
>
> I also had convergence problems calculation quasi-symmetrical 
> structures (for example, numerical frequencies near structures with 
> symmetry higher than C1), and it had nothing to do with excited states.
>
> Regards,
>
> -- 
> Gabriel do Nascimento Freitas
> D.Sc. Student - Graduate Program of Chemistry
> Molecular Modelling and Theoretical Chemistry Laboratory - Room 412
> Chemistry Institute - Universidade Federal do Rio de Janeiro (UFRJ) - 
> Brazil
> (+5521)8830-9971 / (+5521)2562-7179
>
> 2011/11/22 Valérie Vallet <valerie.vallet at univ-lille1.fr 
> <mailto:valerie.vallet at univ-lille1.fr>>
>
>     Dear Joachim,
>
>     We have tried the failsafe option in the casscf block, but this
>     does not improve the CASSCF convergence along the IRC.
>     Could you please modify the molpro code so that we can force the
>     casscf step to restart from HF orbitals?
>     Would it also be possible to offer the possibility to change the
>     step size in the IRC calculation, since this may help improving
>     the CASSCF convergence along the IRC?
>
>     Thanks a lot for your help,
>
>     Valérie
>
>     On Nov 20, 2011, at 5:33 PM, Hans-Joachim Werner wrote:
>
>     > Dear Valérie and Jacky,
>     > I will look at this. This was once changed to make sure that in
>     geometry optimizations it always
>     > uses the same options and starting orbitals from the previous
>     calculation, which is normally most
>     > sensible. I will make an option to disable this behavior. In the
>     meantime you could try the
>     > "FAILSAFE" option, which enables stricter convergence criteria.
>     Perhaps that helps finding the correct
>     > solution.
>     > Best wishes
>     > Joachim
>     >
>     >
>     > --
>     > Prof. Hans-Joachim Werner
>     > Institute for Theoretical Chemistry
>     > University of Stuttgart
>     > Pfaffenwaldring 55
>     > D-70569 Stuttgart, Germany
>     > Tel.: (0049) 711 / 685 64400
>     > Fax.: (0049) 711 / 685 64442
>     > e-mail: werner at theochem.uni-stuttgart.de
>     <mailto:werner at theochem.uni-stuttgart.de>
>     >
>     >
>     >
>     > Am 18.11.2011 um 16:22 schrieb Valérie Vallet:
>     >
>     >> Dear MOLPRO users,
>     >>
>     >> We are trying to run an IRC path at the CASSCF level, and we
>     are facing a case where the automatic CASSCF calculation that uses
>     previous CASSCF orbitals along the reaction coordinate converges
>     to the wrong energy, that is an energy higher than the that one
>     would obtain with a single point calculation using Hartree-Fock
>     orbitals.
>     >>
>     >> We thus would like to force the CASSCF to use HF orbitals
>     instead at each geometry steps. However, it seems that the optg
>     keyword ignores "start" commands in the MCSCF step. Is there an
>     option that allows us to force optg to read "start" instructions?
>     >>
>     >> Thanks a lot for your help,
>     >>
>     >> Valérie Vallet
>     >>
>     >>
>     >>
>     >> ---
>     >> Valérie Vallet
>     >> Research assistant
>     >> Laboratoire PhLAM, CNRS UMR 8523
>     >> Université des Sciences et Technologies de Lille
>     >> Bât P5
>     >> F-59655 Villeneuve d'Ascq, France
>     >> Tel: +33 3 2033 5985 <tel:%2B33%203%202033%205985>
>     >> Fax: +33 3 2033 7020 <tel:%2B33%203%202033%207020>
>     >> E-mail: valerie.vallet at univ-lille1.fr
>     <mailto:valerie.vallet at univ-lille1.fr>
>     >> http://www.phlam.univ-lille1.fr/pub/f/themas/pcmt/
>     >>
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