PROGRAM SUMMARY
Title of program:
GFIT4C
Catalogue identifier:
ADNB
Ref. in CPC:
134(2001)97
Distribution format: tar gzip file
Operating system: AIX 4.1.4.0
High speed store required:
4920K words
Number of bits in a word:
32
Number of lines in distributed program, including test data, etc:
9078
Keywords:
Global potential energy surface (GPES), Tetraatomic systems,
Molecular dynamical calculations, Structure.
Programming language used: Fortran
Computer:
IBM RISC 6000 .
Nature of physical problem:
Given a set of ab initio points of a molecular system with N atoms, the
problem is to obtain a global analytic (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 the part I of this
series we have dealt with triatomic systems and three-dimensional (3D)
representations. In the present part II.1 of this series we treat the
ABCD class of tetraatomic systems and six-dimensional (6D)
representations. The GFIT4C program contains drive code to control the
the five cases for tetraatomic systems. However, in this program, we
have developed the subroutines corresponding to ABCD class. The
following parts II (ABC2, A2B2, AB3 and A4 class of tetraatomic systems
are in preparation), and III (program GFIT5C, for pentaatomic (9D)
systems is in project) should need subroutines from GFIT3C and GFIT4C.
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 some of the authors [2]. Then, the GFIT4C and specific
subroutines of the GFIT3C programs fit the four-body term to the ab
initio values of the tetraatomic system ABCD minus the diatomics and
triatomics potentials evaluated at the corresponding internuclear
distances, using symmetry adapted product functions as for tetraatomic
systems [3]. Similar methods will be used in the following programs of
this series (parts II and III for different classes of tetraatomic and
pentaatomic systems).
Restrictions:
The program GFIT4C is applicable to general tetraatomic systems, i.e.
ABCD class, without nuclei permutational symmetry, but it is also
applicable to tetraatomic systems with several identical nuclei with a
worse behaviour and efficiency than if the permutational symmetry were
taken into account. The subroutines for different classes of
tetraatomic systems with nuclei permutational symmetry will be presented
in the following parts II of this series. The program GFIT4C presented
here is dimensioned for a maximum of 2,000 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 32568 CPU seconds (in an IBM RISC 6000/3CT
workstation) including input/output time.
Unusual features:
Fortran-77 IBM INCLUDE compiler directive is used.
References:
[1] A. Aguado and M. Paniagua. A new functional form to obtain
analytical potentials of triatomic molecules. J. Chem. Phys., 96,
1265-1275 (1992).
[2] A. Aguado, C. Suarez and M. Paniagua. Accurate global fit of the H4
potential energy surface. J. Chem. Phys., 101, 4004-4010 (1994).
[3] A. Aguado, C. Tablero and M. Paniagua. Global fit of ab initio
potential energy surfaces: I. Triatomic systems. Comput. Phys.
Commun. 108, 259-266 (1998).