Robinson Victor Naden, Ghosh Raja, Egan Colin K, Riera Marc, Knight Christopher, Paesani Francesco, Hassanali Ali
The 'Abdus Salam' International Centre for Theoretical Physics, I-34151 Trieste, Italy.
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
J Chem Phys. 2022 May 21;156(19):194504. doi: 10.1063/5.0089773.
Non-polarizable empirical potentials have been proven to be incapable of capturing the mixing of methane-water mixtures at elevated pressures. Although density functional theory-based ab initio simulations may circumvent this discrepancy, they are limited in terms of the relevant time and length scales associated with mixing phenomena. Here, we show that the many-body MB-nrg potential, designed to reproduce methane-water interactions with coupled cluster accuracy, successfully captures this phenomenon up to 3 GPa and 500 K with varying methane concentrations. Two-phase simulations and long time scales that are required to fully capture the mixing, affordable due to the speed and accuracy of the MBX software, are assessed. Constructing the methane-water equation of state across the phase diagram shows that the stable mixtures are denser than the sum of their parts at a given pressure and temperature. We find that many-body polarization plays a central role, enhancing the induced dipole moments of methane by 0.20 D during mixing under pressure. Overall, the mixed system adopts a denser state, which involves a significant enthalpic driving force as elucidated by a systematic many-body energy decomposition analysis.
非极化经验势已被证明无法捕捉高压下甲烷 - 水混合物的混合情况。尽管基于密度泛函理论的从头算模拟可能会规避这一差异，但它们在与混合现象相关的时间和长度尺度方面存在局限性。在此，我们表明，旨在以耦合簇精度再现甲烷 - 水相互作用的多体MB - nrg势，在不同甲烷浓度下，成功捕捉到了高达3 GPa和500 K的这种现象。由于MBX软件的速度和准确性，评估了完全捕捉混合所需的两相模拟和长时间尺度。构建相图上的甲烷 - 水状态方程表明，在给定压力和温度下，稳定混合物的密度比其各部分之和更高。我们发现多体极化起着核心作用，在压力下混合过程中，甲烷的诱导偶极矩增加了0.20 D。总体而言，混合系统呈现出更致密的状态，正如系统的多体能量分解分析所阐明的，这涉及到显著的焓驱动力。
