Local Energy Decomposition of Open-Shell Molecular Systems in the Domain-Based Local Pair Natural Orbital Coupled Cluster Framework.

Ahmet Altun,Frank Neese,Giovanni Bistoni,Masaaki Saitow

doi:10.1021/acs.jctc.8b01145

Abstract

Local energy decomposition (LED) analysis decomposes the interaction energy between two fragments calculated at the domain-based local pair natural orbital CCSD(T) (DLPNO-CCSD(T)) level of theory into a series of chemically meaningful contributions and has found widespread applications in the study of noncovalent interactions. Herein, an extension of this scheme that allows for the analysis of interaction energies of open-shell molecular systems calculated at the UHF-DLPNO-CCSD(T) level is presented. The new scheme is illustrated through applications to the CH2···X (X = He, Ne, Ar, Kr, and water) and heme···CO interactions in the low-lying singlet and triplet spin states. The results are used to discuss the mechanism that governs the change in the singlet–triplet energy gap of methylene and heme upon adduct formation.

Highlights

Weak intermolecular interactions play a major role in virtually all areas of chemical research.[1−6] Perturbative and supermolecular approaches can be used to evaluate weak interaction energies between two or more fragments
The most popular approach of this type is the symmetryadapted perturbation theory (SAPT), which provides a decomposition of the interaction energy into a series of physically meaningful contributions, including electrostatics, induction, London dispersion, and exchange-repulsion terms.[7]
The decomposition of the resulting interaction energy into physical terms is obtained via energy decomposition analysis (EDA) schemes, which are mainly based on a seminal work of Morokuma.[9]

Summary

INTRODUCTION

Weak intermolecular interactions play a major role in virtually all areas of chemical research.[1−6] Perturbative and supermolecular approaches can be used to evaluate weak interaction energies between two or more fragments. The most popular approach of this type is the symmetryadapted perturbation theory (SAPT), which provides a decomposition of the interaction energy into a series of physically meaningful contributions, including electrostatics, induction, London dispersion, and exchange-repulsion terms.[7]. Journal of Chemical Theory and Computation energy decomposition (LED).[38] In this scheme, the interaction energy between two or more fragments is calculated at the DLPNO-CCSD(T) level and is decomposed into a repulsive intramolecular energy term called electronic preparation, plus a series of intermolecular energy terms such as electrostatic, quantum mechanical exchange, and London dispersion interactions.[38] This scheme has been already applied in the context of H-bond interactions,[38,39] frustrated. The presently introduced open-shell variant of the DLPNO-CCSD(T)/LED scheme is applied to a series of prototypical molecular systems (Figure 1) of the type CH2···X, in which methylene

THEORY

COMPUTATIONAL DETAILS

RESULTS AND DISCUSSION

CONCLUSIONS