Non-covalent interactions between molecular dimers (S66) in electric fields

TL;DR

This study systematically analyzes the electric properties of molecular dimers in the S66 set under electric fields, revealing the dominance of electrostatics and evaluating the accuracy of various density functional methods.

Contribution

It provides a detailed quantum chemical analysis of interaction-induced electric properties in molecular dimers, including the effects of different computational methods and basis sets.

Findings

Interaction induced dipole moments are significant mainly in hydrogen-bonded dimers.

Interaction polarizabilities are generally small but have a consistent principal component.

Density functional methods like dRPA@PBE0 closely match coupled cluster results, while PBE alone shows larger errors.

Abstract

We present a systematic study of interaction induced dipole electric properties of all molecular dimers in the S66 set, relying on CCSD(T)-F12b/aug-cc-pVDZ-F12 as reference level of theory. For field strengths up to $\approx$5 GV m$^{-1}$ the interaction induced electric response beyond second order is found to be insignificant. Large interaction dipole moments (i.e. dipole moment changes due to van der Waals binding) are observed in the case of hydrogen bonding oriented along the intermolecular axis, and mostly small interaction dipole moments are found in dimers bonded by $\pi$-stacking or London dispersion. The interaction polarizabilities (i.e. polarizability changes due to van der Waals binding) were generally found to be small but always with a positive-valued principal component approximately aligned with the intermolecular axis, and two other negative-valued components. Energy decompositions according to symmetry adapted perturbation theory (SAPT0/jun-cc-pVDZ) suggest that electrostatics dominates the interaction dipole moment. First-order SAPT0 decompositions into monomer-resolved contributions establish a quantitative link between electric properties of monomers and dimers. Using the aug-cc-pVQZ basis and non-empirical PBE semilocal exchange-correlation kernels, we also assess how density functional approximations in the nonlocal exchange and correlation parts affect the predictive accuracy: While dRPA@PBE0 based predictions are in excellent overall agreement with coupled cluster results, the computationally more affordable LC-$\omega$PBE0-D3 level of theory also yields reliable results with relative errors below 5\%. PBE alone, even when dispersion corrected, produces larger errors in interaction dipole moments and polarizabilities.