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Quadratic String Method for Locating Instantons in Tunneling Splitting Calculations

Cvitaš, Marko Tomislav (2018) Quadratic String Method for Locating Instantons in Tunneling Splitting Calculations. Journal of Chemical Theory and Computation, 14 (3). pp. 1487-1500. ISSN 1549-9618

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The ring-polymer instanton (RPI) method is an efficient technique for calculating approximate tunneling splittings in high-dimensional molecular systems. In the RPI method, tunneling splitting is evaluated from the properties of the minimum action path (MAP) connecting the symmetric wells, whereby the extensive sampling of the full potential energy surface of the exact quantum-dynamics methods is avoided. Nevertheless, the search for the MAP is usually the most time-consuming step in the standard numerical procedures. Recently, nudged elastic band (NEB) and string methods, originaly developed for locating minimum energy paths (MEPs), were adapted for the purpose of MAP finding with great efficiency gains [J. Chem. Theory Comput. 2016, 12, 787]. In this work, we develop a new quadratic string method for locating instantons. The Euclidean action is minimized by propagating the initial guess (a path connecting two wells) over the quadratic potential energy surface approximated by means of updated Hessians. This allows the algorithm to take many minimization steps between the potential/gradient calls with further reductions in the computational effort, exploiting the smoothness of potential energy surface. The approach is general, as it uses Cartesian coordinates, and widely applicable, with computational effort of finding the instanton usually lower than that of determining the MEP. It can be combined with expensive potential energy surfaces or on-the- fly electronic-structure methods to explore a wide variety of molecular systems.

Item Type: Article
Additional Information: This work has been fully supported by Croatian Science Foundation under the project IP-2014-09-7540.
Uncontrolled Keywords: semiclassical ; instanton ; tunneling splittings ; water clusters
Subjects: NATURAL SCIENCES > Chemistry
NATURAL SCIENCES > Chemistry > Theoretical Chemistry
Divisions: Division of Physical Chemistry
Project titleProject leaderProject codeProject type
Novo poglavlje u procesima prijenosa naboja u vodenimi otopinama-CTPAMRIvan LjubićIP-2014-09-7540HRZZ
Depositing User: Marko-Tomislav Cvitaš
Date Deposited: 02 Dec 2019 15:53
DOI: 10.1021/acs.jctc.7b00881

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