Ring-Polymer Instanton Tunneling Splittings of Tropolone and Isotopomers using a ?-Machine Learned CCSD(T) Potential: Theory and Experiment Shake Hands

• Type of Material: Article
• Authors: Apurba Nandi, Emory University; Gabriel Laude, ETH Zürich; Subodh S Khire, RIKEN Center for Computational Science; Nalini D Gurav, University of Münster; Chen Qu, Independent Researcher, Toronto M9B0E3, Canada; Riccardo Conte, Università Degli Studi di Milano; Qi Yu, Yale University; Shuhang Li, Emory University; Paul L Houston, Cornell University; Shridhar R Gadre, Savitribai Phule Pune University; Jeremy O Richardson, ETH Zürich; Francesco Evangelista, Emory University; Joel Bowman, Emory University
• Language: English
• Date: 2023-04-20
• Publisher: AMER CHEMICAL SOC
• Publication Version: Final Published Version
• Copyright Statement: © 2023 The Authors. Published by American Chemical Society
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1021/jacs.3c00769
• Title of Journal or Parent Work: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
• Volume: 145
• Issue: 17
• Start Page: 9655
• End Page: 9664
• Keywords: ATOM TRANSFER; Science & Technology; FORMIC-ACID; INFRARED-SPECTROSCOPY; Physical Sciences; PROTON-TRANSFER; Chemistry; LARGE MOLECULES; Chemistry, Multidisciplinary; ENERGY SURFACE; H-ATOM; FTIR SPECTRUM; DYNAMICS; GROUND-STATE
• Research Categories: Chemistry, Biochemistry

Abstract

Tropolone, a 15-atom cyclic molecule, has received much interest both experimentally and theoretically due to its H-transfer tunneling dynamics. An accurate theoretical description is challenging owing to the need to develop a high-level potential energy surface (PES) and then to simulate quantum-mechanical tunneling on this PES in full dimensionality. Here, we tackle both aspects of this challenge and make detailed comparisons with experiments for numerous isotopomers. The PES, of near CCSD(T)-quality, is obtained using a Δ-machine learning approach starting from a pre-existing low-level DFT PES and corrected by a small number of approximate CCSD(T) energies obtained using the fragmentation-based molecular tailoring approach. The resulting PES is benchmarked against DF-FNO-CCSD(T) and CCSD(T)-F12 calculations. Ring-polymer instanton calculations of the splittings, obtained with the Δ-corrected PES are in good agreement with previously reported experiments and a significant improvement over those obtained using the low-level DFT PES. The instanton path includes heavy-atom tunneling effects and cuts the corner, thereby avoiding passing through the conventional saddle-point transition state. This is in contradistinction with typical approaches based on the minimum-energy reaction path. Finally, the subtle changes in the splittings for some of the heavy-atom isotopomers seen experimentally are reproduced and explained.