Subject: Qeq & others charge equilibration method

From: Didier MATHIEU <[email-masked]>
Date: Thu, 15 Jan 1998 10:37:39 +0100

Dear colleagues

I recently learned through this electronic list that the Qeq
equilibration method of A.K. Rappe et al. is used by a commercial MSI
product called WebLab 2.0. 

I currently need a very fast method to estimate the molecular
electrostatic potential outside de Van der Waals surface, preferably
avoiding QM calculations, and turn to empirical charge equilibrations
methods. Finally I consider using the QEq scheme, but maybe I could
benefit from the experience of some of us, especially if s.O. already
studied MEP built from QEq charges ?? The modified PEOE scheme by the
team of Sheraga is illustrated with the MEP of formamide, but it seems
oriented to popypeptides ? ...

On the other hand, as mentionned in the original paper in J.Phys.Chem.
the QEq charges might in principle be used to estimated IR or Raman
intensities. Did anybody test such an empirical scheme, or try to
improve on this basis ? I am also interested in empirical (i.e. fast)
simulations of IR & Raman spectra, but I don't know whether is is
possible to get meaningful intensities without prohibitive ab initio
calculations.

Finally, I am interested in any information that could provide me with a
feeling of what can be expected from the various empirical charge
equilibration models (PEOE, FEOE, Qeq...) available so far, and to know
more about all their other possible applications (as reactivity indices
maybe ?)

Thanks to all netters for the interesting information exchanged on CCL.
Regards

Narushi Goto wrote:
> The partial atomic charges of a given molecules are calculated using
> QEq (Charge equilibration method) based on this article.
>  A.K., Goddard, W.A., Charge Equilibration for Molecular Dynamics
> Simulations, J. Phys. Chem., 95, 3358, 1991

At 4:04 PM 98.1.5, Hr. Dr. S. Shapiro wrote:
> Dear Colleagues;
>
>         Does anyone know how the partial atomic charges are calculated
>using MSI's
> WebLab 2.0?  s it the Gasteiger-Marsili procedure, or is some other 

-- 
Didier MATHIEU
CEA - Le Ripault, BP 16
37260 Monts (France)
Tel. 33(0)2.47.34.41.85