From: Francesco Pietra (chiendarret_at_gmail.com)
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

francesco

On Thu, Aug 20, 2015 at 7:23 PM, Mayne, Christopher G <cmayne2_at_illinois.edu>
wrote:

> Francesco,
>
> I responded here:
> http://www.ks.uiuc.edu/Research/vmd/mailing_list/vmd-l/26205.html
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ks.uiuc.edu_Research_vmd_mailing-5Flist_vmd-2Dl_26205.html&d=AwMFAg&c=8hUWFZcy2Z-Za5rBPlktOQ&r=-HlUTO-p5cBc5PIIWOaJ9-qnT28s75DUp7XlPlRi7DY&m=hckOdtohvEupU4CfzeFwAxpXzxhSco3vdYrhq7bfK9I&s=9Hol9P12g2oVy9_qFjZrZcrKadtHwLIAIthlZ1QQJtI&e=>
>
> 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--