From: Francesco Pietra (
Date: Thu Aug 20 2015 - 12:50:55 CDT

Hi Chris:
Sorry for having missed your answer. I also came across those suggestions
by Gaussian, but that was not the reason. As I said it was lack of
sufficient memory.

I still have to become comfortable with "divide and conquer". As it is
implied in your answer that it is of such accuracy as to demand OPT/MP2,
I'll try to learn how to do.

At any event, would ffTK accept the Gaussian log file from geometry
optimization at SCF level, followed by single-point MP2? Or is ffTK
expecting a log for geometry optimization at MP2 level?

Thanks a lot


On Thu, Aug 20, 2015 at 7:23 PM, Mayne, Christopher G <>

> Francesco,
> I responded here:
> <>
> MP2 is the level of theory prescribed by the CHARM General Force Field to
> accurately describe the internal dynamics of molecule. Further, it is
> generally accepted practice to take a "divide and conquer" approach to
> parameterize large ligands.
> Regards,
> Christopher Mayne
> On Aug 20, 2015, at 10:13 AM, Francesco Pietra wrote:
> Hello:
> I posted recently about ffTK OPT MP2 problems, no answer, however it
> became clear that the shared memory on a node (120GB) was not enough, and
> could not be increased. On the other hand, Gaussian is threaded, so that I
> can't exploit the enormous resources of the cluster.
> Therefore, my question is, is OPT at MP2 really needed for getting a good
> ff for ligands along ffTK in the realm of classical MD? OPT at SCF level,
> followed by single-point MP2 is not enough? I understand that it depends on
> what one is looking for, from simple docking to normal mode calculations,
> so that my question covers all situations.
> If SCF followed by single-point MP2 is not enough, the only alternative
> that I can see is to break the ligand into pieces and carry out OPT/MP2 on
> each piece, allowing for the approximations in reforming the whole ligand--e89a8f23573905cad2051dc1cb05--