Effect of basis set superposition error on the electron density of molecular complexes

The Chemical Hamiltonian Approach (CHA) versions of the Roothaan and Kohn-S ham equations, labeled CHA/F and CHA/DFT, respectively, have been used to o btain the basis set superposition error (BSSE)-corrected first-order electr on density of the hydrogen fluoride dimer with several basis sets. We have analyzed the effect of BSSE in terms of the electronic relaxation, i.e., th e redistribution of the electron density due to the inclusion of the CHA co rrection at a frozen geometry, along with the subsequent nuclear relaxation process. Critical points of the charge density have been located and chara cterized to compare the conventional, uncorrected first-order electron dens ity against the BSSE-corrected density at each level of theory. Contour dif ference maps between BSSE-corrected and uncorrected densities on the molecu lar plane have also been plotted to gain insight into the effects of BSSE c orrection on the electron density. (C) 2000 American Institute of Physics. [S0021-9606(00)31423-4].