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Benchmark ab initio and dynamical characterization of the stationary points of reactive atom + alkane and SN2 potential energy surfaces

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Abstract

We describe a composite ab initio approach to determine the best technically feasible relative energies of stationary points considering additive contributions of the CCSD(T)/complete-basis-set limit, core and post-CCSD(T) correlation, scalar relativistic and spin–orbit effects, and zero-point energy corrections. The importance and magnitude of the different energy terms are discussed using examples of atom/ion + molecule reactions, such as X + CH4/C2H6 and X + CH3Y/CH3CH2Cl [X, Y = F, Cl, Br, I, OH, etc.]. We test the performance of various ab initio levels and recommend the modern explicitly-correlated CCSD(T)-F12 methods for potential energy surface (PES) developments. We show that the choice of the level of electronic structure theory may significantly affect the reaction dynamics and the CCSD(T)-F12/double-zeta PESs provide nearly converged cross sections. Trajectory orthogonal projection and an Eckart-transformation-based stationary-point assignment technique are proposed to provide dynamical characterization of the stationary points, thereby revealing front-side complex formation in SN2 reactions and transition probabilities between different stationary-point regions.

Graphical abstract: Benchmark ab initio and dynamical characterization of the stationary points of reactive atom + alkane and SN2 potential energy surfaces

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Article information


Submitted
05 Sep 2019
Accepted
06 Dec 2019
First published
06 Dec 2019

Phys. Chem. Chem. Phys., 2020, Advance Article
Article type
Perspective

Benchmark ab initio and dynamical characterization of the stationary points of reactive atom + alkane and SN2 potential energy surfaces

G. Czakó, T. Győri, B. Olasz, D. Papp, I. Szabó, V. Tajti and D. A. Tasi, Phys. Chem. Chem. Phys., 2020, Advance Article , DOI: 10.1039/C9CP04944D

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