Distinguishing homolytic versus heterolytic bond dissociation of phenyl sulfonium cations with localized active space methods

TL;DR

This paper demonstrates that localized active space SCF (LASSCF) methods can effectively model bond dissociation in phenyl sulfonium cations, providing smooth potential energy surfaces and insights into homolytic versus heterolytic pathways.

Contribution

The study applies LASSCF to chemical reactions, showing it produces smooth energy profiles and comparable results to CASSCF with less computational cost.

Findings

LASSCF yields smooth potential energy scans.

LASSCF predicts similar bond energies to CASSCF.

Homolytic cleavage for di- and triphenylsulfonium, heterolytic for monophenylsulfonium.

Abstract

Modeling chemical reactions with quantum chemical methods is challenging when the electronic structure varies significantly throughout the reaction, as well as when electronic excited states are involved. Multireference methods such as complete active space self-consistent field (CASSCF) can handle these multiconfigurational situations. However, even if the size of needed active space is affordable, in many cases the active space does not change consistently from reactant to product, causing discontinuities in the potential energy surface. The localized active space SCF (LASSCF) is a cheaper alternative to CASSCF for strongly correlated systems with weakly correlated fragments. The method is used for the first time to study a chemical reaction, namely the bond dissociation of a mono-, di-, and triphenylsulfonium cation. LASSCF calculations generate smooth potential energy scans more easily than the corresponding, more computationally expensive, CASSCF calculations, while predicting similar bond dissociation energies. Our calculations suggest a homolytic bond cleavage for di- and triphenylsulfonium, and a heterolytic pathway for monophenylsulfonium.