Khanna Vikram, Doherty Michael F, Peters Baron
Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, California 93106, USA.
Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, USA.
J Chem Phys. 2020 Dec 7;153(21):214504. doi: 10.1063/5.0025844.
Solid-fluid phase equilibria are difficult to predict in simulations because bound degrees of freedom in the crystal phase must be converted to free translations and rotations in the fluid phase. Here, we avoid the solid-to-fluid transformation step by starting with chemical potentials for two reference systems, one for the fluid phase and one for the solid phase. For the solid, we start from the Einstein crystal and transform to the fully interacting molecular crystal. For the fluid phase, we introduce a new reference system, the "centroid," and then transform to gas phase molecules. We illustrate the new calculations by predicting the sublimation vapor pressure of succinic acid in the temperature range of 300 K-350 K.
固-液相平衡在模拟中很难预测，因为晶相中的束缚自由度必须转化为流体相中的自由平移和旋转。在这里，我们通过从两个参考系统的化学势开始，避免了从固体到流体的转变步骤，一个参考系统用于流体相，另一个用于固体相。对于固体，我们从爱因斯坦晶体开始，然后转变为完全相互作用的分子晶体。对于流体相，我们引入了一个新的参考系统“质心”，然后转变为气相分子。我们通过预测琥珀酸在300 K-350 K温度范围内的升华蒸气压来说明新的计算方法。
