Re: some recommendations for parametrizing new molecules required

From: Axel Kohlmeyer (
Date: Fri Jan 23 2009 - 09:25:01 CST

On Fri, 23 Jan 2009, Christopher Gillespie wrote:

CG> Hi Vlad,


CG> I have recently started a parameterization of my own and here is what I have
CG> seen thus far.
CG> GAMESS supposedly has decent parallelization and potentially can be faster
CG> than Gaussian. I say supposedly because I have only tried it once and have
CG> used Gaussian for everything else. Gaussian has parallelization as well but
CG> I have been informed GAMESS does a better job of it. Also, I have used the
CG> US version and have not tried another.
CG> As for time, I have a 43 atom optimization (MP2/cc-PVDZ) with counterpoise
CG> correction running for the last 13 days with Gaussian, which is higher than
CG> the recommended HF/6-31g* level for CHARMM FFs but still your system is
CG> quite a bit larger, QM speaking.

now that looks like a nice waste of computer time. have you at
least preoptimized the structure with HF/6-31g*? have you
checked how much of a difference you would get by cranking
up the basis set? have you considered, that in many cases
hybrid DFT gives you similar "quality" results than MP2 at
a fraction of the cost, particularly with larger systems,
due to different scaling behavior. have you considered, that
the extra level of theory is of limited use, since you want
to fit a classical potential and the resulting error will
probably outweigh the difference in error between the HF
and the MP2 run?


CG> Hopefully someone with more GAMESS experience can supply more information on
CG> its speed and use with Paratool.
CG> Best
CG> Chris

Axel Kohlmeyer
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
If you make something idiot-proof, the universe creates a better idiot.

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