Subject: HBFF/SVD fot fitting FF constants problem

From: "Hui-Hsu (Gavin) Tsai" <[email-masked]>
Date: Fri, 23 Oct 1998 13:50:59 -0500

Dear all,

    I try to use Hessian biased singular value decomposition (HBFF/SVD)
method to optimize the potential form and Force Field constants to
perform the vibration frequency calculations of some medium size
molecules.  This method is based on singular value decomposition (SVD)
of Jacobian which is the partial derivatives in force(F) and Hessian(H)
with respect to FF parameters (geometry (c) and force constants (k) ).
The Jacobian matrix has four main componets

[ dF/dc, dF/dk ]
[ dH/dc, dH/dk],

with [dH/dc,dH/dk] being much smaller than [ dF/dc, dF/dk].

  My question is as below:

   Because of the different magnitudes of the components of the Jacobian
matrix, the step change for the carestian coordinates is acceptable, but
is very SMALL for the force contsnts.  I multiplied the step change of
force constants by a scaling factor, but it is not very efficient
because of their different magnitudes ( e.g. stretching force constants
>> bending force constants >> cross term force constants). Is there any
suggestions on how to nondimensitionize this Jacobian Matrix?

   Any suggestions will be welcomed and appreciated.

Gavin Tsai