[gmx-users] QMMM free energy

[David Mobley]

I think Erik is right, here. In a QM sense, what does it mean to have
an atom that is halfway in between, say, hydrogen and carbon?

You might want to look at what Wei Yang at Florida State has been
doing. If I remember correctly he has been making some efforts towards
QM/MM free energy calculations...

David


On 5/30/07, Erik Lindahl <lindahl at cbr.su.se> wrote:
> Hi,
>
> I'm not a QM expert myself (Gerrit, comments?),  but I'm pretty sure
> the main reason is that you cannot either mutate atom types or
> decouple interactions gradually in the QM part of the system. Once
> this is solved for a pure QM system it should be straightforward to
> implement the QM/MM interface of it.
>
> Cheers,
>
> Erik
>
> On May 30, 2007, at 5:30 PM, Robert fiske wrote:
>
> >> With the original QM/MM implementation, free energy is currently
> >> not possible (yet). From what you report, I guess that also with
> >> the CPMD interface it does not work.
> >
> > The CPMD interface is mostly plugged into the same setup as the
> > other QM interfaces, I was able to bypass the error by copying
> > modifying the free energy else statement to bypass the vdw
> > calculations for the case of bQMMM true (and generally try to have
> > that code match the bQMMM case of non free energy runs).  But since
> > my background is Computer Engineering and not chemistry (Chemistry
> > 101 is as far as I got in formal training)  I don't really know
> > what should be done (I assume since as you said it's not
> > implemented yet although I don't get a run time error that the
> > results will be off).
> >
> > Are QM/MM free energy calculations substantially different than MM
> > calculations, or is it just not implemented because no one has
> > needed to do QM/MM with free energy yet?
> >
> >
> > fiske
> > Gogonea Group
> > Cleveland State University
> >
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