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Manuscript Title: A Fortran 90 Hartree-Fock program for one-dimensional periodic π-conjugated systems using Pariser-Parr-Pople model
Authors: Kondayya Gundra, Alok Shukla
Program title: ppp_bulk.x
Catalogue identifier: AEKW_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 183(2012)677
Programming language: Fortran 90.
Computer: PCs and workstations.
Operating system: Linux, Code was developed and tested on various recent versions of 64-bit Fedora including Fedora 14 (kernel version
Keywords: Hartree-Fock method, self-consistent field approach P-P-P model Hamiltonian, Periodic boundary conditions.
PACS: 31.15.xr, 31.15.Ne, 31.15.bu, 31.15.-p.
Classification: 7.3.

External routines: This program needs to link with LAPACK/BLAS libraries compiled with the same compiler as the program. For the Intel Fortran Compiler we used the ACML library version 4.4.0, while for the gfortran compiler we used the libraries supplied with the Fedora distribution.

Nature of problem:
The electronic structure of one-dimensional periodic π-conjugated systems is an intense area of research at present because of the tremendous interest in the physics of conjugated polymers and graphene nanoribbons. The computer program described in this paper provides an efficient way of solving the Hartree-Fock equations for such systems within the P-P-P model. In addition to the Bloch orbitals, band structure, and the density of states, the program can also compute quantities such as the linear absorption spectrum, and the electro-absorption spectrum of these systems.

Solution method:
For a one-dimensional periodic π-conjugated system lying in the xy-plane, the single-particle Bloch orbitals are expressed as linear combinations of pz-orbitals of individual atoms. Then using various parameters defining the P-P-P Hamiltonian, the Hartree-Fock equations are set up as a matrix eigenvalue problem in the k-space. Thereby, its solutions are obtained in a self-consistent manner, using the iterative diagonalizing technique at several k points. The band structure and the corresponding Bloch orbitals thus obtained are used to perform a variety of calculations such as the density of states, linear optical absorption spectrum, electro-absorption spectrum, etc.

Running time:
Most of the examples provided take only a few seconds to run. For a large system, however, depending on the system size, the run time may be a few minutes to a few hours.