On accurate estimations for H/D isotope effects at super-cold conditions: Path Integral Molecular Dynamics (PIMD) simulations

        D/H ratios serve as a key toolkit for tracing water and organics in forms of gases, liquids and ices. Therefore, accurate estimations for H/D isotope effects during the formation and transfer for these H-incorporated compounds at super-cold conditions (around 10 to 200 K) with different phases (gas, liquid and solid) are urged. We have developed theoretical protocols for gaseous molecules in a previous work [1] by introducing the so-called full partition function ratios (FPFRs). However, such methods are rather complex and unpractical for condensed systems such like water ices, liquid methane and so on. In this study, we developed new protocols for accurate estimations of these equilibrium H/D isotope fractionations especially for condensed systems (e.g., water, ices) by combining path integral molecular dynamics (PIMD) simulations (modified for improving its convergence at low temperatures) with deep potentials (DP) obtained with machine learning. Preliminary results will be introduced and discussed.   References: [1] Zhang Y. N. and Liu Y. 2018. Geochim. Cosmochim. Acta. 238, 123.