Chapter 7: Instanton Theory to Calculate Tunnelling Rates and Tunnelling Splittings
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Published:22 Sep 2020
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Special Collection: 2020 ebook collection
V. Zaverkin and J. Kästner, in Tunnelling in Molecules: Nuclear Quantum Effects from Bio to Physical Chemistry, ed. J. Kästner and S. Kozuch, The Royal Society of Chemistry, 2020, ch. 7, pp. 245-260.
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Instanton theory is a rigorous semiclassical theory to calculate tunnelling rate constants and tunnelling splittings of vibrational levels, taking movements of all atoms of a molecular system into account. Rate constants are obtained from the imaginary part of the free energy of a metastable quantum state. The free energy, in turn, is derived from partition functions calculated via Feynman's path integral formulation of quantum mechanics. Its usage has tremendously increased over the last decade in chemistry and surface science. This chapter discusses its basic foundations, its derivation, advantages and limits in applications.