Subject: Point Q's & Benzen Quadrupole

From: "Gustavo A. Mercier Jr" <[email-masked]>
Date: Fri, 25 Jul 1997 12:57:58 -0400 (EDT)

HI!

In the Cornell et al. paper describing the latest AMBER force field
a statement is made about ESP (particularly RESP) charges for
Benzene reproducing the electric quadrupole accurately.
The Qc=-Qh=-0.145 a.u.

I have a publication that measures the dilute solution quadrupole.
The value is listed as Quad(zz)=-2Quad(xx)= -28e-40 Cm^2

Using,
    Quad(zz) = Sum[i] Qi((Zi)^2 - (Ri)^2)

where (Ri)^2 = (Xi)^2 + (Yi)^2 + (Zi)^2

I fail to reproduce the value.

The Cornell paper does not give the reference to the Quad(zz) they
used.

Anybody can help in resolving this discrepancy. Is there another
value published for Quad(zz) that is radically different? like
a gas phase value?

Thanks for any help!
bye

-- 
                                      ("`-/")_.-'"``-._
Gustavo A. Mercier,Jr.,MD,PhD         (. . `) -._    )-;-,_() 
Division of Nuclear Medicine          (v_,)'  _  )`-.\  ``-
Dept. of Radiology                    _;- _,-_/ / ((,'
University of Pennsylvania           ((,.-'  ((,/
3400 Spruce St.                  [email-masked]
Philadelphia, PA 19104         215-662-3069/3091 fax: 215-349-5843