Subject: CCL: deriving CFF91 partial charges

From: "Dr. Bruno Catalanotti" <brucatal)at(unina.it>
Date: Fri, 04 Feb 2005 17:24:55 +0100

dear CCLers,
I am trying to parametrize a protonated quinoline-based moiety with  the 
CFF91 Force Field (Insight2000.1 environment). CFF91 is not able to 
delocalize the additional charge on the aromatic ring, giving rise to 
the warning: "total formal charge does not equal total partial charge." 
In the case of CVFF Force Field, Accelrys suggests  to derive partial 
charges of protonated compounds  by comparing partial charges assigned 
by CVFF force field with those calculated by a MNDO semi-empirical 1 SCF 
calculations performed on the neutral and the ionized compounds.

Can anyone suggest me:
1 which semiempirical method is more suitable to derive CFF91 - 
compatible partial charges?
2 some references regarding methods to modify force field assigned 
partial charges?
3 any other alternative methods to calculate partial charges ?

Thank you in advance for help,
Best regards,
Bruno