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  • Incorporating reduced axis system embedding into ab initio tunnelling-rotation Hamiltonians with curvilinear vibrational Møller–Plesset perturbation theory
Title: Incorporating reduced axis system embedding into ab initio tunnelling-rotation Hamiltonians with curvilinear vibrational Møller–Plesset perturbation theory
Large-amplitude vibrational motion influences the rovibrational structure of molecules that tunnel between multiple wells. Reaction path (RP) Hamiltonians, and curvilinear coordinates more gen- erally, are useful for modelling pure vibrational motion in these systems and provide a practical framework for calculating accurate ab initio anharmonic vibrational energies and tunnelling split- tings with perturbation theory. These computational tools also offer the means to address rotation- vibration coupling associated with large-amplitude motion in rotating molecules. In this paper, we incorporate the reduced axis system (RAS) frameembeddingwithRPHamiltoniansandsecond-order vibrational Møller-Plesset perturbation theory (VMP2). Because the RP-RAS Hamiltonian eliminates rotation-vibration momentumcoupling everywhere along a one-dimensional reaction path, it is well suited for rovibrational VMP2 methods, the convergence of which relies critically on approximate vibration-vibration and vibration-rotation separability. The accuracy of this combined RP-RAS-VMP2 scheme is demonstrated by comparisons with numerically exact variational calculations and VMP2 parameters based on traditional Eckart embeddings for reduced-dimension models of torsional tunnelling in hydrogenperoxideandinversion tunnelling in cyclopropyl radical. Thefavourablecom- putational scaling ofVMP2makes it a promising strategy for calculating accurate tunnelling-rotation parameters for medium-sized and larger molecules in full dimensionality.  more » « less
Award ID(s):
2110489
PAR ID:
10528750
Author(s) / Creator(s):
Publisher / Repository:
Taylor & Francis
Date Published:
Journal Name:
Molecular Physics
Volume:
2024
ISSN:
0026-8976
Page Range / eLocation ID:
e2304098
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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