Fortran 90 implementation of the Hartree-Fock approach within the CNDO/2 and INDO models

TL;DR

This paper presents a Fortran 90 program implementing the Hartree-Fock method within CNDO/2 and INDO semi-empirical models, enabling efficient calculations of large molecular systems including fullerenes and polymers.

Contribution

The paper introduces a computationally efficient Fortran 90 code for Hartree-Fock calculations using CNDO/2 and INDO models, capable of handling large molecules like C60 and polymers.

Findings

Efficient calculations on large molecules like C60 within seconds.

The program computes molecular orbitals, energies, and properties such as dipole moments.

Application to diverse systems including small molecules, fullerenes, and polymers.

Abstract

Despite the tremendous advances made by the ab initio theory of electronic structure of atoms and molecules, its applications are still not possible for very large systems. Therefore, semi-empirical model Hamiltonians based on the zero-differential overlap (ZDO) approach such as the Pariser-Parr-Pople, CNDO, INDO, etc. provide attractive, and computationally tractable, alternatives to the ab initio treatment of large systems. In this paper we describe a Fortran 90 computer program developed by us, that uses CNDO/2 and INDO methods to solve Hartree-Fock(HF) equation for molecular systems. The INDO method can be used for the molecules containing the first-row atoms, while the CNDO/2 method is applicable to those containing both the first-, and the second-row, atoms. We have paid particular attention to computational efficiency while developing the code, and, therefore, it allows us to perform calculations on large molecules such as C_60 on small computers within a matter of seconds. Besides being able to compute the molecular orbitals and total energies, our code is also able to compute properties such as the electric dipole moment, Mulliken population analysis, and linear optical absorption spectrum of the system. We also demonstrate how the program can be used to compute the total energy per unit cell of a polymer. The applications presented in this paper include small organic and inorganic molecules, fullerene C_60, and model polymeric systems, viz., chains containing alternating boron and nitrogen atoms (BN chain), and carbon atoms (C chain).