Localized Orbitals for Incremental Evaluations of the Correlation Energy within the Domain-Specific Basis Set Approach.

Abstract

A modified version of the Boys localization method is proposed in order to make the domain-specific basis set approach in the framework of the incremental scheme (J. Chem. Phys. 2008, 129, 244105) generally applicable. The method optimizes the molecular orbitals in one atomic orbital basis set to be similar to localized molecular orbitals in a second atomic orbital basis set under the constraint that the molecular orbitals stay orthonormal. The procedure is tested for RI-MP2 incremental correlation energy expansions for aromatic systems like naphthalene, anthracene, and tetracene as well as for conjugated hydrocarbon chains like C20H2, C20H22, or p-quaterphenyle. For all investigated systems, a rapid convergence of the incrementally expanded correlation energies to the exact RI-MP2 energies is found. Furthermore, the systematic improvability of the approach is demonstrated.