Quantitative assessment of the effect of basis set superposition error on the electron density of molecular complexes by means of quantum molecular similarity measures

Pedro Salvador,Xavier Fradera,Miquel Duran

doi:10.1002/qua.22039

Abstract

AbstractThe Chemical Hamiltonian Approach (CHA) method is applied to obtain Basis Set Superposition Error (BSSE)‐free molecular orbitals at the Hartree–Fock (HF) and Density Functional Theory (DFT) levels of theory. To assess qualitatively the effect of the BSSE on the first‐order electron density, we had previously applied Bader's analysis of the intermolecular critical points located on the electron density, as well as density difference maps for several hydrogen bonded complexes. In this work, Quantum Molecular Similarity Measures are probed as an alternative avenue to properly quantify the electronic relaxation due to the BSSE removal by means of distance indices between the uncorrected and corrected charge densities. It is shown that BSSE contamination is more important at the DFT level of theory, and in some cases, changes on the topology of the electron density are observed upon BSSE correction. Inclusion of diffuse functions have been found to dramatically decrease the BSSE effect in both geometry and electron density. The CHA method represents a good compromise to obtain accurate results with small basis sets. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Highlights

W hen studying intermolecular interactions with finite basis sets, one must face the socalled Basis Set Superposition Error (BSSE) [1]
The general structure and molecular connectivity are preserved for all calculations, the level of theory, basis set, and BSSE correction have a significant impact on the molecular geometry
The effect of the BSSE on the electron density of two prototypical weakly bound molecular complexes has been evaluated by comparing electron densities obtained with conventional ab initio HF and Density Functional Theory (DFT) methodologies and the corresponding Chemical Hamiltonian Approach (CHA)/F and CHA/DFT methods, which correct the BSSE in the wavefunction itself

Summary

Introduction

W hen studying intermolecular interactions with finite basis sets, one must face the socalled Basis Set Superposition Error (BSSE) [1]. This unphysical effect is deeply related to the ab initio methods, based on the linear combination of atomic orbitals (LCAO), together with the use of the supermolecular approach. Under this approximation, the interaction energy is trivially determined as the energy difference between the complex and their isolated fragments. The electronic redistribution associated to the removal of BSSE cannot be analyzed within the CP framework

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