Comparison of Precise Electronic Charge Densities and Electrostatic Potentials Obtained from Different AB INITIO Approaches

Abstract

The treatment of molecular systems via standard ab initio methods requires the use of a large amount of computational resources. With present ab initio techniques, it is possible to obtain electronic charge densities and electrostatic potentials at the HF and MP2 levels of theory, restricted however to about 250 basis functions for the HF and about 100 for the MP2 calculations. The most sophisticated level of theory for computing charge densities and electrostatic potentials within the Gaussian 88 program is the MP2/6-311++G(3df,3pd) procedure. Unfortunately, its use is only feasible for molecules containing up to 2 or 3 atoms. As an alternative solution for calculating precise electronic charge densities and electrostatic potentials, we now have access to methods based on Local Density Functional theory1. These schemes produce very accurate electronic charge densities and electrostatic potentials at a relatively low cost in computer resources (N³ for LDF against N⁴ for HF and N⁵ for MP2); the results compare in quality with the best standard ab initio calculations.