On Tue, Jan 24, 2017, Marek Maly wrote:
>
> I have technical question regarding QM methods used in GAFF2 development.
cc-ing to Junmei Wang, who doesn't always follow the mailing list. Note that
you may need to wait for the paper on GAFF2 to be published...
...dac
>
> In Amber16 manual, page 286, there is written:
>
> "We have performed B3LYP/6-31G* optimization for 15 thousands marketed or
> experimental ..."
>
>
> So B3LYP/6-31G* is here QM method used to obtain optimized molecular
> structures (low energy
> conformations) from which equilibrium geometrical terms (eq. bond lengths,
> eq. angles) were obtained
> and so in some cases old GAFF values were updated.
>
>
> But in GAFF2, comparing to GAFF, changed clearly also some force constants.
> As an example I can mention c3-c3 bond:
>
>
> In GAFF
> c3-c3 300.9 1.5375 SOURCE1_SOURCE5 88072 0.0058
>
> In GAFF2
> c3-c3 232.52 1.538 SOURCE1_SOURCE5 88072 0.0058
>
>
> My question is, which QM methodology was used to derive (perhaps using
> paramfit ?) new GAFF2 bond, angle or dihedral force constants ?
>
> I assume, that since here we need just to calculate for each conformation
> only it's
> energy (no optimization) and since we also need to obtain reliable force
> constants (hence we need accurate QM energies) some more accurate method
> was probably used like MP2/6-31G** , MP3/6-31G** etc. to derive QM
> energies. Am I right ?
>
> So thank you in advance for QM methodology specification used in GAFF2 for
> force constants
> derivation.
>
> Best wishes,
>
> Marek
>
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Received on Tue Jan 24 2017 - 11:00:02 PST
