AN EFFICIENT METHOD FOR CALCULATING STATIC POLARIZABILITIES FROM A CORRELATED WAVE-FUNCTION

We present a method closely related to configuration interaction over single excitations (CI-S) for the calculation of static dipole moments and polarizabilities, which we call modified configuration interactio n over single excitations (MCI-S). This method allows for orbital rela xation through the inclusion of single excitations on a correlated fir st-order Rayleigh-Schrodinger wave function. An approximation to our M CI-S results in an inexpensive method to calculate polarizabilities th at yields good results when compared with the full configuration inter action (CI-F) results. This method, called modified configuration inte raction over single excitations without triple excitations (MCI-S_WT), seems particularly suitable to applications for large systems. Exampl es are presented using the intermediate neglect of the differential ov erlap model Hamiltonian (INDO/1), which indicates that the MCI-S-WT pr ocedure presents an error of less than 15% with respect to the CI-F va lues in a fraction of the computational effort. (C) 1994 John Wiley an d Sons, Inc.