PRACTICAL EXPRESSIONS FOR THE 2-CENTER MULTIPOLE EXPANSION OF R(12)(-1)

An explicit and transparent deduction of a conventional expression for the two-center multipole expansion of the Coulomb potential, r(12)(-1 ), in terms of spherical harmonics, is performed. An intermediate expr ession in the deduction is shown to be well suited for transformation into a Cartesian representation. Practical formulas are produced that allow for safe and efficient implementations in computer programs. Ele ctrostatic interactions between two pairs of point charges are compute d and the importance to include the higher multipole interactions is s tressed. (C) 1995 John Wiley & Sons, Inc.