ON THE RAPID EVALUATION OF COFACTORS IN THE CALCULATION OF NONORTHOGONAL MATRIX-ELEMENTS

The calculation of matrix elements involving nonorthogonal orbitals is speeded up by recognizing the orthogonalities between orbitals,leadin g to generalized Slater rules. The block structure present in the over lap matrix makes an efficient evaluation of its cofactors possible. Th ese cofactors are calculated per subblock, each with its own parity si gn. An adjustment parity sign has to be evaluated, which is added to t he combined local signs, to give the correct total sign for the matrix element. An algorithm for the evaluation of this adjustment sign has been developed, making an easy and correct evaluation possible. The cu rrent scheme is shown to be very efficient, but possibilities for furt her improvement remain. (C) 1998 John Wiley & Sons, Inc.