A Fortran 90 Hartree-Fock program for one-dimensional periodic $\pi$-conjugated systems using Pariser-Parr-Pople model

TL;DR

This paper introduces a Fortran 90 program that employs the Pariser-Parr-Pople model to solve Hartree-Fock equations for one-dimensional periodic pi-electron systems, enabling calculations of band structures, optical spectra, and effects of external electric fields.

Contribution

The paper presents a novel Fortran 90 code capable of modeling electronic properties of infinite 1D pi-conjugated systems using the P-P-P model, including external field effects.

Findings

Computed band structures and optical spectra for polymers and nanoribbons.

Simulated effects of external electric fields on electronic properties.

Validated the code with known systems like polyacetylene and graphene nanoribbons.

Abstract

Pariser-Parr-Pople (P-P-P) model Hamiltonian is employed frequently to study the electronic structure and optical properties of $\pi$-conjugated systems. In this paper we describe a Fortran 90 computer program which uses the P-P-P model Hamiltonian to solve the Hartree-Fock (HF) equation for infinitely long, one-dimensional, periodic, $\pi$-electron systems. The code is capable of computing the band structure, as also the linear optical absorption spectrum, by using the tight-binding (TB) and the HF methods. Furthermore, using our program the user can solve the HF equation in the presence of a finite external electric field, thereby, allowing the simulation of gated systems. We apply our code to compute various properties of polymers such as $trans$-polyacetylene ($t$-PA), poly-\emph{para}-phenylene (PPP), and armchair and zigzag graphene nanoribbons, in the infinite length limit.