[molpro-user] optimization restart

Ricardo Mata rmata at cii.fc.ul.pt
Thu Apr 2 09:49:01 BST 2009

Dear Zdenek,

In a QM/MM implementation you need a program for computing the QM
gradient (in your case Molpro), a program for the MM gradient (in your
case Amber) and some subroutines which can:

a) call both programs,
b) retrieve the two gradients,
c) build the total QM/MM gradient,
d) based on the gradient do an optimization step and
e) go back to step a)

Apparently, you have written some routines for steps a)-c), and want
to use Molpro optimization routines to do d), I guess... my question
would be, why?

Since Molpro is a QM program, it has been coded to handle small
systems. Surely you can change the default maximum number of atoms
(200), but if you are working with more than a thousand atoms, you
have to input a gradient for those thousand atoms. This would require
a new compilation, using an extremely large number of maximum atoms. I
wouldn't advise you to do so. The normal procedure when building a
QM/MM interface is either to write your own optimizer, or perhaps to
use the MM program, which contrary to Molpro has been coded to handle
large systems. It may even have some handy tools for optimization
(like hybrid cartesian-internal coordinates algorithms).

Also, if you happen to take a look at the Molpro manual, OPTG is for
automatic optimizations, that means, you deliver the control to Molpro
and he will call the gradient program and perform optimization steps
until he finds a minimum. What you were looking for is another keyword
which you will likewise find described in the Manual.

But again, it is unwise to use Molpro for step d).

Best wishes,

On Wed, Apr 1, 2009 at 10:37 AM, Zdenek Futera <futera.zd at centrum.cz> wrote:
> Hello!
> I try implement interface between Molpro (ver. 2006.1) and Amber in
> order to do QM/MM calculations (it is script based system similar to
> ChemShell). During QM/MM optimization I calculate energy and gradients
> on some structure then I change these gradients according to QM/MM
> scheme and then I need to restart Molpro from these gradients and
> compute new structure.
> I found out that gradients are saved in restart file 1 in record 700 and
> I can rewrite them there. Is it possible to restart from this changed
> file 1, read coordinates and gradients and compute only new coordinates?
> I guess I have to change source code, because when I try restart OPTG
> procedure new gradients are calculated from the last structure in file
> 1. Is there any easier way than change the source code? And if not which
> part of the source code should I change to do it in easiest way? Could
> you please give me an advice?
> Best regards
> Zdenek Futera
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