Coupled cluster theory with the polarizable continuum model of solvation

Abstract

The environment may significantly affect molecular properties. Thus, it is desirable to account explicitly for these effects on the wave function and its derivatives, especially when the latter are evaluated with accurate methods, such as those belonging to coupled cluster (CC) theory. In this tutorial review, we discuss how to combine CC methods with the polarizable continuum model of solvation (PCM). We describe useful approximations that include the solvent response to the correlation and excited state equations while maintaining the computational cost comparable to in vacuo calculations. Although applied to PCM, the theoretical framework presented in this review is general and can be used with any polarizable embedding model. Representative applications of the CC-PCM method to ground and excited state properties of solvated molecules are presented, and comparisons with experiment, and between the full and approximate schemes are discussed.coupled cluster, PCM, excited states, linear response, state specific 1 | INTRODUCTION Many experimental measurements of chemical processes, from reactivity to spectroscopy, are performed in solution. Theoretical simulations of these phenomena require the use of quantum mechanical (QM) methods to study the electronic behavior. However, these methods involve a considerable computational effort so that the QM region can often only include the solute and possibly a few solvent molecules. Bulk effects cannot be easily reproduced quantum mechanically, and often they do not need to. The main polarization effects of the solvent on the solute electron density can be reproduced with classical solvation models, where the solute-solvent interaction is added to the solute Hamiltonian via an effective one-electron operator. In general, classical solvation models can be divided in two families: implicit and explicit models. The former replace the atomistic description of the solvent with a continuum polarizable medium, and they are computationally very efficient since the solvent response is introduced through a macroscopic quantity of the solvent, that is, the dielectric permittivity. The downside is that direct solute-solvent interactions like hydrogen bonding cannot be described, although continuum models are usually better than the corresponding calculation in vacuo. [1] Conversely, explicit solvation models retain an atomistic representation of the solvent molecules, which are usually treated with a classical force field (MM) that may or may not be polarizable. Explicit models are more realistic, but they require considerable computational effort to ensure proper sampling of the solvent configuration space, which requires the repetition of the QM/MM calculations over many snapshots obtained from a molecular dynamics (MD) simulation. The choice between implicit and explicit models is often based on a compromise between cost and accuracy for the property of interest.This tutorial review is concerned with the interface of coupled cluster (CC) methods, [2,3] among the most accurate but e...

Dielectric continuum methods for quantum chemistry

“…This review is focused on the theoretical framework and computational mechanics of continuum solvation models, not on applications. Some limited data are provided in order to describe the performance of the models, but the reader is directed to several general reviews for a more complete overview of continuum solvation methods in action 8,13–15,26–28 . Other, more specialized reviews describe the application of PCMs to specific types of spectroscopy 29–35 .…”

Single‐reference coupled cluster methods for computing excitation energies in large molecules: The efficiency and accuracy of approximations

“…The latter also reported a mixed implicit/explicit EOM solvent model as well as benchmark results on PCM–EOM . Caricato's recent review is also a useful guide to the field . It should be noted that when PCM is added, the EOM and linear response treatments yield different results .…”

“…It should be noted that when PCM is added, the EOM and linear response treatments yield different results . In particular, the latter depends on the transition density of the solute and can be recommended for the description of transition properties, while in the former approach the solvent responds to the excited state density of the solute and thus it is also called state specific since for each state it provides a better description of the mutual polarization between solute and solvent . A different implicit solvent model, the conductor‐like screening model (COSMO) was also implemented for the ADC(2) method recently .…”

Asymmetry in the Qy Fluorescence and Absorption Spectra of Chlorophyll a Pertaining to Exciton Dynamics

“…All calculations reported in the main text are performed in the gas phase. Treatments of solvent through implicit and/or explicit methods can be very successful (Hush and Reimers, 2000 ; Tomasi, 2011 ; Mennucci, 2012 ; Skyner et al, 2015 ; Zuehlsdorff and Isborn, 2018 ; Caricato, 2019 ; Cerezo et al, 2020 ), but no such approach has been demonstrated as yet to be successful for understanding chlorophyll bandshapes. Indeed, results presented in Supplementary Table 1 using commonly applied solvation treatments fail to provide qualitatively useful information, as has been previously noted for bacteriochlorophyll-a (Higashi et al, 2014 ).…”