PROGRAM SUMMARY
Title of program:
GFIT4C-2
Catalogue identifier:
ADOV
Ref. in CPC:
140(2001)412
Distribution format: tar gzip file
Operating system: AIX 4.1.4.0
High speed store required:
12K words
Number of bits in a word:
32
Number of lines in distributed program, including test data, etc:
13560
Keywords:
Global potential energy surface (GPES), Tetratomic systems,
Molecular dynamical calculations, Structure.
Programming language used: Fortran
Computer:
IBM RISC 6000/3CT .
Nature of physical problem:
Given a set of ab initio points of a molecular system with N atoms, the
problem is to obtain a golbal analytical (3N - 6)-dimensional
representation of the corresponding adiabatic potential having all the
symmetry properties of the system and satisfying the stringent criteria
[1] needed in molecular dynamical calculations. In Part II.1 [4] of
this series we have dealt with the tetratomic system class ABCD and
six-dimensional (6D) representation (program GFIT4C). In the present
Part II.2 we treat A2B2 and ABC2 tetratomic system classes and 6D
representations (program GFIT4C-2) that are invariant with respect to
permutations of two equivalent nuclei.
The GFIT4C program contains drive code to control the five cases for
tetratomic systems. However, in the program here reported, we have
developed the subroutines corresponding to ABC2, and A2B2 system
classes. The following versions of the program (Parts II.3 and II.4 of
this series) deal with the AB3 and A4 system classes of tetratomic
molecules, giving potentials that are invariant with respect to
permutations of three and four equivalent nuclei, respectively. These
new versions are in preparation.
Method of solution:
The method of solution consists in expressing the potential as a
many-body expansion choosing as variables the internuclear distances.
The program sequentially fits all the two and three-body terms in the
many-body expansion to the corresponding ab initio data for all the
possible diatomics and triatomics molecules, using the functional form
proposed by part of the authors [2]. Then, the GFIT4C program fits the
four-body term to the ab initio values of the tetratomic system
(including system classes A2B2, ABC2 and ABCD in the version GFIT4C-2 of
the program) minus the diatomics and triatomics potentials evalued at
the corresponding internuclear distances, using symmetry adapted product
functions.
Restrictions:
These new subroutines of the program GFIT4C are only applicable to
tetratomic A2B2 and ABC2 system classes, with permutational symmetry
between two identical nuclei, but it is also applicable to tetratomic
systems with more than two identical nuclei (whose subroutines will be
presented in Parts II.3 and II.4 of this series) with a worse behaviour
and efficiency than if the whole permutational symmetry were taken into
account. These new subroutines are needed also to run the following
programs GFIT5C of the corresponding series for pentatomic systems. The
program GFIT4C is dimensioned for a maximum of 2000 ab initio points and
a maximum degree of 15 for the two-body fitting polynomials and 10 for
the three- and four-body fitting polynomials. However, the dimension
corresponding to the number of ab initio points may be enlarged easily
by modifying the value of "NMAX" parameter in the file dimensions.inc.
Typical running time:
For the test deck is about 2065 and 2298 CPU seconds (in an IBM RISC
6000/3CT workstation) including input/output time for the A2B2 and ABC2
system classes.
Unusual features:
Fortran-77 IBM INCLUDE compiler directive is used.
References:
[1] A. Aguado, M. Paniagua, A new functional form to obtain analytical
potentials of triatomic molecules, J. Chem. Phys. 96 (1992)
1265-1275.
[2] A. Aguado, C. Suarez, M. Paniagua, Accurate global fit of the H4
potential energy surface, J. Chem. Phys. 101 (1994) 4004-4010.
[3] A. Aguado, C. Tablero, M. Paniagua, Global fit of ab initio
potential energy surfaces: I. Triatomic systems, Comput. Phys.
Comm. 108 (1998) 259-266.
[4] A. Aguado, C. Tablero, M. Paniagua, Global fit of ab initio
potential energy surfaces: II.1. Tetraatomic systems ABCD, Comput.
Phys. Comm. 134 (2001) 97-109.