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arXiv 2104.08326cond-mat.mtrl-scicond-mat.mes-hallcond-mat.softcond-mat.stat-mech
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用关联函数和多体势计算Carbon Dioxide的Phase Diagram

The Phase Diagram of Carbon Dioxide from Correlation Functions and a Many-body Potential

Amanda A. Chen, Alexandria Do, Tod A. Pascal

摘要:

本文用分子动力学(MD)模拟和两相热力学(2 PT)方法研究了125 - 325 K和1 - 10,000 atm下CO2的相稳定性和相平衡。我们设计了一个直接的方法来计算相图一般,通过考虑单独的化学势的孤立相在特定点上的P-T图。因此,2 PT精确且有效地近似液体的熵和吉布斯能的独特能力允许从相对短($\mathrm{\sim}$ 100 ps)的MD模拟分配相边界。我们通过计算柔性基本物理模型2(FEPM 2)的临界特性来验证我们的方法,与以前的结果吻合得很好。然而,我们发现,短程泡利力的不正确的描述和缺乏分子电荷极化导致在高压下的实验偏差。因此,我们开发了一个多体,波动电荷模型CO ${}_{2}$,称为CO ${}_{2}$ -Fq,从高层次的量子力学(QM)计算,准确地捕捉到凝聚相的振动特性的固体(包括费米共振在1378厘米${}^{-1}$)以及液体的扩散性能,导致整体优秀的协议与实验在整个相图。这项工作提供了一个有效的计算方法来确定任意系统的相图,并强调量子力学电荷重组物理在分子相稳定性的关键作用。

英文摘要:

The phase stability and equilibria of carbon dioxide is investigated from 125 -- 325K and 1 -- 10,000 atm using extensive molecular dynamics (MD) simulations and the Two-Phase Thermodynamics (2PT) method. We devise a direct approach for calculating phase diagrams in general, by considering the separate chemical potentials of the isolated phase at specific points on the P-T diagram. The unique ability of 2PT to accurately and efficiently approximate the entropy and Gibbs energy of liquids thus allows for assignment of phase boundaries from relatively short ($\mathrm{\sim}$ 100ps) MD simulations. We validate our approach by calculating the critical properties of the flexible Elementary Physical Model 2 (FEPM2), showing good agreement with previous results. We show, however, that the incorrect description of the short-range Pauli force and the lack of molecular charge polarization leads to deviations from experiments at high pressures. We thus develop a many-body, fluctuating charge model for CO${}_{2}$, termed CO${}_{2}$-Fq, from high level quantum mechanics (QM) calculations, that accurately captures the condensed phase vibrational properties of the solid (including the Fermi resonance at 1378 cm${}^{-1}$) as well as the diffusional properties of the liquid, leading to overall excellent agreement with experiments over the entire phase diagram. This work provides an efficient computational approach for determining phase diagrams of arbitrary systems and underscore the critical role of QM charge reorganization physics in molecular phase stability.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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