Chapter 3 - Intermolecular Interaction Energies from Kohn–Sham Random Phase Approximation Correlation Methods

Abstract

The random-phase approximation (RPA) based on Kohn–Sham (KS) reference states is presented as a ground-state electron correlation method to describe the electron correlation contributions to intermolecular interaction energies in this chapter. While originally the RPA was developed to describe the collective properties of electrons in the homogeneous electron gas, it will be shown that the method can also be used with some success to characterize the noncovalent bonding of molecular systems. This will be demonstrated by testing the RPA and several extensions to it in a number of benchmark sets for intermolecular interactions, including small to medium-sized dimer systems. Furthermore, the application of KS-RPA methods in intermolecular perturbation theory, for the description of σ- and π-stacking interactions of hydrocarbon complexes, and their capability to describe large supramolecular host–guest complexes is also highlighted. It is shown that KS-RPA methods can deliver a higher accuracy for intermolecular interaction energies than standard density-functional theory (DFT) methods including empirical dispersion corrections. Due to the reduced computational cost to standard ab-initio wave function methods beyond second-order (in the electron–electron interaction) KS-RPA methods therefore fill a gap between fast but too imprecise DFT methods and highly accurate but expensive wave function approaches. Furthermore, unlike common DFT methods, KS-RPA methods can be systematically improved as will be shown by comparing intermolecular interaction energies from the bare RPA method with two extensions to it which include electron exchange interactions beyond first order.