The Laplacian of the electronic density at the valence-shell charge concentration (VSCC): A comparative study of effective core potential and full-electron calculations in Mo compounds. II

The effective core potential (ECP), using a basis set of different qualities, and ab initio full-electron (FE) calculations were carried out for MoS⁻²₄, MoO⁻²₄, and MoOCl₄ molecules. The topology of − ▿²p(r_cp) (the negative Laplacian of the charge density at its critical points) in the atomic valence shell was studied. Results clearly indicate that semicore (ECP2) approaches are able to reproduce, in a qualitative way, the topology of the Laplacian distribution with respect to those obtained by the FE method. Modifications of basis sets, such as introduction of polarization functions on the ligands, affect the electronic charge distribution (number of critical points in MoOCl₄) for FE as well as for ECP2 approaches. The ECP2 scheme predicts correctly the order of − ▿²p_x(r_cp) (X = O, S, Cl, Mo) in the valence shell; nevertheless, it fails in the relative magnitudes of − ▿²p_Mo(r_cp) between Mo compounds in respect to FE calculations. A scaling factor consistently improves the values of − ▿²p(r_cp) and p(r_cp), which are larger than those obtained with FE, particularly the − ▿²p(r_c) values. © 1996 John Wiley & Sons, Inc.