The Role of d Functions in Ab Initio Calculations. 11. The Deformation Densities of SOZ, NOa, and Their Ions.

Comparison of the optimized geometries and SCF energies for the series XO;, XOz, XO;, XOZ -* with X = S,N shows that d(S) functions cause larger bond shortening and energy drop than d functions centered on first-row atoms. This is further emphasized On comparing the separate effects of d(centra1 atom) and d(O) functions for SO2 and NO;, which are similar only for the first-row molecule. The d(S) functions are also essential for proper prediction of the OSO angles. The deformation densities calculated for each series and the corresponding X-0 shared populations, change as expected on adding electrons first into CT* then into r* molecular orbitals. In the regions aro.und nuclei the deformation densities express the behavior of the atomic s and p valence orbitals or of their product inside their radial nodes.