AMBER Archive (2003)

Subject: Re: AMBER: Re:atomic charges and internal H-bond

From: Jiri Sponer (sponer_at_ncbr.chemi.muni.cz)
Date: Tue Oct 07 2003 - 15:48:00 CDT

I am not sure whether spurious CT is the problem
unless these are particularly strong H-bonds,
though I can not rule out this.
It may be related to the ESP method of charge
derivation.
To get an idea about CT one might try for example Natural Bond Orbitak
charge analysis, and, as you suggest, to compare with
more flexible basis set, better covering the space.
SCF itself underestimates deformation of molecules upon
H-bonding and thus reduces CT type of contributions.

Jiri

>
> As Piotr pointed out spurious charge transfer is a problem. Using
> a bigger basis set(and a method better than HF) can reduce the problem
> (though then the charge will not be consistent with the
> RESP protocol HF/6-31G*).May be you can try to get charges using
> two different basis sets (and different methods) and see
> how different they are.
>
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