Approximate Molecular Orbital Calculations A short computer program (183 source cards, 8K bytes, 8 X 8 matrices) has been written in Fortran IV, to perform approximate moleculer orbital calculations. Essentially the program calculates the eigen values and vectors of the secular determinant IH - ESI = 0. In solvine this determinant two o ~ t i o n sare available. (1) The matrix S is considered the unit matttrk (i.e., ovkrlap is ignored) and (2) non-zero off-dia&nal values areallowed in's (i.e., overlap is included). Using either option the resonance integrals are approximated by Hij = B Sij. Input data. include the proportionality constant 8, the overlap matrix (upper triangle), coulomb integrals (Hii values), thenumber of atomicorhitals, and a.pammeter specifying theoptiondesired. Theoutput consists of headings, H and S matrices in full, the data. parameters, and the eigen values and vectors in ascending order. The program is of special interest due to its simplicity and versatility. For students with a limited mathematical background the subroutine (115 source cards) calculating the eigen values and vectors, by i,he Jacobi method, may be considered a "black box" and the remainder of the program gives an insight into molecular orbital hheory and Fortran IV programming. The program is versatile since problems from the simple homonuclear diatomic molecule, without overlap, to calculations with up to eight different coulomb integrals, with overlap, may he solved. Hiickel type calculations may be treated, as a. special case, without difficulty. Copies of the program will be gladly sent on request.
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Journal o f Chemical Education
