Direct path integral estimators for isotope fractionation ratios

Abstract

Fractionation of isotopes among distinct molecules or phases is a quantum effect which is often exploited to obtain insights on reaction mechanisms, biochemical, geochemical and atmospheric phenomena. Accurate evaluation of isotope ratios in atomistic simulations is challenging, because one needs to perform a thermodynamic integration with respect to the isotope mass, along with time-consuming path integral calculations. By re-formulating the problem as a particle exchange in the ring polymer partition function, we derive new estimators giving direct access to the differential partitioning of isotopes, which can simplify the calculations by avoiding thermodynamic integration. We demonstrate the efficiency of these estimators by applying them to investigate the isotope fractionation ratios in the gas-phase Zundel cation, and in a few simple hydrocarbons.

arXiv comment13 pages, 7 figures

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Cited by in corpus (10)

• Nuclear quantum effects enter the mainstream
• Ab initio thermodynamics of liquid and solid water
• High Order Path Integrals Made Easy
• Quantum-mechanical exploration of the phase diagram of water
• Routine Molecular Dynamics Simulations Including Nuclear Quantum Effects: from Force Fields to Machine Learning Potentials
• Accelerating quantum instanton calculations of the kinetic isotope effects
• A combined on-the-fly/interpolation procedure for evaluating energy values needed in molecular simulations
• Accelerating equilibrium isotope effect calculations: I. Stochastic thermodynamic integration with respect to mass
• Computing chemical potentials of adsorbed or confined fluids
• Accelerating equilibrium isotope effect calculations: II. Stochastic implementation of direct estimators