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[Licence| Download | New Version Template] aefw_v1_0.tar.gz(496 Kbytes)
Manuscript Title: A general purpose Fortran 90 electronic structure program for conjugated systems using Pariser-Parr-Pople model
Authors: Priya Sony, Alok Shukla
Program title: ppp.x
Catalogue identifier: AEFW_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 181(2010)821
Programming language: Fortran 90. Compilers used: Program has been tested with Intel Fortran Compiler (noncommercial version 11.1) and gfortran compiler (gcc version 4.4.0) with optimization option -O.
Computer: PCs, workstations.
Operating system: Linux. Code was developed and tested on various recent versions of Fedora including Fedora 11 (kernel version 2.6.29.4-167).
Keywords: Hartree-Fock method, self-consistent field approach PPP model Hamiltonian, Molecular orbitals.
Classification: 7.3, 16.1.

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 4.3.0, while for gfortran compiler we used the libraries supplied with the Fedora distribution.

Nature of problem:
The problem of interest at hand is the electronic structure of π-conjugated systems. For such systems, the effective π-electron P-P-P semi-empirical model Hamiltonian proposed by Pariser, Parr, and Pople offers an attractive alternative as compared to the ab initio approaches. The present program can solve the HF equations for both open- and closed-shell systems within the P-P-P model. Moreover, it can also include electron correlation effects at the singles CI level. Along with the wave functions and energies, various properties such as linear absorption spectra can also be computed.

Solution method:
The single-particle HF orbitals of a π-conjugated system are expressed as linear combinations of the pz-orbitals of individual atoms (assuming that the system is in the xy-plane). Then using the hopping and Coulomb parameters prescribed for the P-P-P method, the HF integro-differential equations are transformed into a matrix eigenvalue problem. Thereby, its solutions are obtained in a self-consistent manner, using the iterative diagonalizing technique. The HF orbitals thus obtained can be used to perform a variety of calculations such as the SCI, linear optical absorption spectrum, polarizabilty, electro-absorption spectrum, etc.

Running time:
The examples provided each only take a few seconds to run. For a large molecule or a polymer, however, the run time may be a few minutes.