Abstract
The quadrupole moments (Θ) of the molecules P2, S2 and Cl2 have been computed at the SCF, CASSCF and CASSCF + 1 + 2 levels of theory, using augmented correlation consistent basis sets. The convergence of Θ as a function of basis set and level of theory is discussed. The variation of Θ from the separated atoms to the equilibrium region is reported. Θ is written as the sum of a sigma and pi contribution, and inaccuracies in the SCF values for P2 and S2 are due to the poor representation of the pi system in the SCF theory. A reference state dependent quadrupole moment density, - ½(3cos2 θ- 1)r 2δη(r; R), is defined whose integral is the mole2 cular quadrupole moment, and the spatial distributions of the density and its relationship to the density difference δη(r; R) are examined.