Fortran programming for curve fitting and improving quality of intermolecular pair potential function

Abstract

The program MRQFIT version 1.0 has been developed in order to fit and improve quality of intermolecular pair potential function. This program implements in Fortran language using FORTRAN-77 on UNIX-system. In the curve fitting step, the stabilization energies of the complex which have been calculated by means of quantum chemical calculations are fitted using a multidimensional non-linear least-squares procedure by the Levenberg-Marquardt algorithm. In the step of function improvement, the quality of the function is examined using Beveridge algorithm, and then, the false minima which may be available in the function are searched. In this study, the Li+-NH3 and NH3-NH3 systems are used to develop and test the program. It is clearly seen that the energies obtained from the function are in good agreement with the SCF energies, especially for the attractive regions. The program can be used to fit interaction energies to a functional form and improve quality of the function between the two molecules.