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655. GRID: Point Multipoles Derived from Molecular
Electrostatic Properties (Version 3.0)
by Christophe Chipot and Janos G. Angyan, Laboratoire
de Chimie Theorique, Universite de Nancy I, BP. 239,
54506 Vand-uvre-les-Nancy Cedex, France
GRID 3.0 is a major functionality revision of version
2.0. This program derives point charges and dipoles
from molecular electrostatic properties computed by
GAUSSIAN 88, 90, 92 and 92/DFT.
The ab initio or semi-empirical electrostatic
properties are evaluated on a grid of discrete points
surrounding the molecule. This grid may be built
employing two alternative approaches:
Standard Cox and Williams type sampling algorithm
(subroutine pnt). The selection of points for
the fitting procedure implies the construction of
an initial parallelepiped-shaped grid of spaced
points. The dimensions of the grid containing
the molecule involve an exclusion radius on all
sides. Points found to lie further than rmax (an
arbitrarily chosen distance defining the grid
boundaries) from any nucleus are discarded.
Points inside the so-called van der Waals
envelope are also rejected. Because of the
short-range effects of electron cloud
penetration, which generally prevents a correct
representation of the SCF potential by point
charge models, the size of this envelope has been
doubled. The density of points used for the fit
may be modified by adjusting the grid step +r.
It has been observed that there is no noticeable
influence of this density on the fitted charges,
as long as the space surrounding the molecule is
sampled properly.
GEPOL algorithm (subroutine gepol). The selection
of points is achieved by generating van der Waals
surfaces around the molecule. Since, in this
procedure, the number of points per van der Waals
sphere is limited to 60, the use of a simple
envelope proved to be insufficient to yield
acceptable charges. For this reason, it is
necessary to construct a series of concentric van
der Waals envelopes separated by a grid step +r.
The minimal distance of the furthermost envelope
is defined by the parameter rmax. Just like in
subroutine pnt, the size of the envelope is over-
dimensioned to avoid the deleterious effects of
penetration.
After running this section of GRID, a sequential access
fort.52 file written in the (3F20.12) format is
generated. This file containing the Cartesian
coordinates of the grid points (in Angstroms) is used
by the GAUSSIAN suite of programs, which, in turn,
create a fort.53 file that includes, depending on the
chosen option, the molecular electrostatic potential
and its successive derivatives (in atomic units).
Point charges are derived by means of a least-squares
fitting procedure.
Lines of Code: 6705
FORTRAN 77
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