New Program for Approximate Molecular Orbital Calculations A generalized version of the computer program to perform approximate molecular orbital calculations has been written.' The original program calculated the eigenvalues and vectors of the secular determinant IH - ESI = 0, where the resonance integrals were approximated by H t j = 0St,. The generalized version allows any values of the resonance integrals to he used and, if required, the density matrix is calculated and a population analysis is performed. The charge distribution and the ionization potential (Kaopmans' Theorem) are also determined. These optional results are printed along with the headings, the H and S matrices in full, and the eigenvalues and vectors in ascending order. As with the original program, no Longer available, the generalized program is simple and versatile and is written in Fortran W. The input includes a heading card, followed by a card with the number of atomic orbitals, a parameter indicating whether overlap is to be included or not and a third parameter, which is zero if the density matrix and other additional results are not requested: otherwise this parameter is the number of occupied molecular orbitals. The program consists of 224 cards, 117 of these belong to a subroutine which finds the eigenvalue solution of the double-symmetric matrix system.The program is small, -10K for up t o 8 X 8 matrices. Copies of the program, along with examples varying from homonuelear diatomin without overlap to polystomie systems with overlap, will he gladly sent on request. 1 Fitzpatrick,
N., J. CHEM. EDUC., 49,344 (1972).
Noel J. Fitzpatrick University College Belfield Dublin 4. Ireland
Volume 57. Number 10. October 1974
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