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.

13 pages, 7 figures

References in corpus (4)

• Efficient stochastic thermostatting of path integral molecular dynamics
• Full dimensional (15D) quantum-dynamical simulation of the protonated water-dimer II: infrared spectrum and vibrational dynamics
• Efficient first-principles calculation of the quantum kinetic energy and momentum distribution of nuclei
• Quantum fluctuations and isotope effects in ab initio descriptions of water

Cited by in corpus (4)

• Quantum-mechanical exploration of the phase diagram of water
• Accelerating quantum instanton calculations of the kinetic isotope effects
• Accelerating equilibrium isotope effect calculations: I. Stochastic thermodynamic integration with respect to mass
• Computing chemical potentials of adsorbed or confined fluids