Experimental Versus Theoretical Electron Densities. Small Molecules, Large Molecules, and Salts

Abstract

High quality ab initio calculations of electron deformation densities and comparisons with available experimental results are presented for small molecules. AHF (approximate Hartree-Fock) basis set and electron correlation effects are assessed. The high quality of the 4-31G + BF (bond functions) basis set for the computation of deformation densities is established for small molecules. Comparison of 4-31G + BF electron densities with all available experimental data is made for some selected large organic molecules. Errors and problems in the experimental and theoretical methods are discussed. Crystal effects such as hydrogen bonding and ion effects in salts are estimated. It is shown that all the effects considered (i.e., near HF basis set, correlation, hydrogen bonding and ion effects) are small compared to possible experimental uncertainties. Thus, at present, economical 4-31G + BF calculations of isolated molecules are sufficiently accurate for comparisons with any type of experimental determination in gas or solid phases.