Karl & Francois,
Sorry about that. The 6-31++G** basis set is for (d,p) not (2d,2p).
I meant 6-31++G(2d,2p).
The only issue with making a standard method for GLYCAM charge
development is ensuring that exocyclic rotamers are frozen in their MD
value. Otherwise your setup is fine. Note that there is the
potential to use HF/cc-pvtz with a RESP weight of 0.0005 for GLYCAM as
well. We tend to avoid this for charge development on large molecules
but this is what we use for charge development in small molecules.
Both cc-pvtz (RESP weight 0.0005) and 6-31G* (RESP weight of 0.01)
produce very similar charges.
-Matt
On Fri, Sep 23, 2011 at 8:12 AM, FyD <fyd.q4md-forcefieldtools.org> wrote:
> Dear Karl,
>
>> I have one small correction to point out. Much of Glycam06's
>> energetic parametrization on neutral molecules was done using
>> B3LYP/6-31++G(2d,2p) single-point calculations, performed on
>> HF/6-31G(d) optimized geometries - not B3LYP/6-31++G**. This use of
>> this theory and larger basis set comes from N.L. Allinger's study of
>> carbohydrate energies (Lii et al J. Comput. Chem, 1999, 20, 1593),
>> and is pointed out in the 2007 Glycam06 paper. The use of the basis
>> set is important, since hybrid DFT results are very dependent upon
>> the basis used.
>
> ok thanks a lot for the update...
>
> Concerning charge derivation (& NOT energy values):
> Geometry optimization is carried out using HF/6-31G(d)... as in Cieplak et al.
>
> See http://q4md-forcefieldtools.org/REDS/popup/popkeyword.php
> -1- RESP-A1A
> HF/6-31G*//HF/6-31G* - Connolly surface algo. used in MEP computation
> - 2 stage RESP fit qwt=0.0005/0.001
> Used in the Cornell et al., Kollman et al., Cheatham et al., Wang et
> al. & Hornak et al. AMBER force fields
>
> -5- RESP-C2
> HF/6-31G*//HF/6-31G* - CHELPG algo. used in MEP computation - 1 stage
> RESP fit qwt=0.01
> Used in the GLYCAM force fields
>
> With R.E.D. Server (and R.E.D.-III.x & IV), we would like to propose
> the exact theory level used by the authors of a published method
> (HF/6-31G* for Cieplak et al., HF/6-31G** for Duan et al., and so...
> HF/6-31G* for Kirschner et al.; i.e. what we currently propose - it
> makes sense) by default i.e. when using R.E.D. III.x/IV & its mode 1
> (http://q4md-forcefieldtools.org/REDS/popup/popredmodes.php).
>
> Then, any user - if she/he does not like the original approach - can
> increase the theory level used in geometry optimization when using the
> R.E.D. III.x/IV mode 2; i.e. by providing her/his own geometry
> optimization output obtained with her/his own basis set choice...
>
> regards, Francois
>
>
>
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>
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Received on Fri Sep 23 2011 - 11:00:02 PDT
