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Instanton theory of ground-state tunneling splittings with general paths

Eraković, Mihael; Vaillant, Christophe L.; Cvitaš, Marko Tomislav (2020) Instanton theory of ground-state tunneling splittings with general paths. Journal of Chemical Physics, 152 (8). ISSN 0021-9606

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We derive a multidimensional instanton theory for calculating ground-state tunneling splittings in Cartesian coordinates for general paths. It is an extension of the method by Mil’nikov and Nakamura [J. Chem. Phys. 115, 6881 (2001)] to include asymmetric paths that are necessary for calculating tunneling splitting patterns in multi- well systems, such as water clusters. The approach avoids multiple expensive matrix diagonalizations to converge the fluctuation prefactor in the ring- polymer instanton (RPI) method, and instead replaces them by an integration of a Riccati differential equation. When combined with the string method for locating instantons, we avoid the need to converge the calculation with respect to the imaginary time period of the semiclassical orbit, thereby reducing the number of convergence parameters of the optimized object to just one: the number of equally spaced system replicas used to represent the instanton path. The entirety of the numerical effort is thus concentrated in optimizing the shape of the path and evaluating hessians along the path, which is a dramatic improvement over RPI. In addition to the standard instanton approximations, we neglect the coupling of vibrational modes to external rotations. The method is tested on the model potential of malonaldehyde and on the water dimer and trimer, giving close agreement with RPI at a much-reduced cost.

Item Type: Article
Uncontrolled Keywords: instanton theory ; tunneling splittings ; path-integral methods ; quantum molecular dynamics ; rovibrational states
Subjects: NATURAL SCIENCES > Chemistry
Divisions: Division of Physical Chemistry
Project titleProject leaderProject codeProject type
Novo poglavlje u procesima prijenosa naboja u vodenim otopinama-CTPAMRIvan LjubićIP-2014-09-7540HRZZ
Svjetlo na molekulama: istraživanje spregnute elektronske i nuklearne dinamike-LightMolNađa DošlićIP-2016-06-1142HRZZ
Depositing User: Marko-Tomislav Cvitaš
Date Deposited: 01 Oct 2020 14:26
DOI: 10.1063/1.5145278

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