Energy and entropy decomposition using the electron density

Abstract

Chemists often classify chemical interactions as being dominated by some sort of interaction; among the most popular and useful classifications are steric, polarization, charge-transfer, electron-pairing, and electrostatic interactions. In real molecular processes, of course, each of these effects contributes, although often one dominates. This talk will focus on how one may use density-functional theory (DFT) to define, quantify, and compute these interactions. The most straightforward approach is DFT-based energy decomposition analysis; this provides a full decomposition of the energy into steric, polarization, charge-transfer, electrostatic, and electron-pairing (covalent bond formation) contributions. One advantage of the DFT-based approach is that it is insensitive to basis set and it can be applied at any level of theory (beyond single Slater determinants). Another approach is based on partitioning the Kullback- Liebler entropy into charge-transfer (“mixing”) and polarization (“deformation”) terms. Both approaches can be combined with a Hirshfeld-style population analysis method. Unlike many other approaches, these methods appear to provide a clean (but obviously nonunique) separation between charge-transfer and polarization effects