High Temperature and Pressure Equation of State Models for Natural Fluids in the System NaCl-KCl-CaCl2-H2O-CO2-CH4

该研究计划将有助于发展状态方程（EOS），该方程可用于准确预测与地球过程相关的宽PTX范围内NaCl-KCl-CaCl2-H2O-CO2-CH4 （SWG）体系的热力学性质（例如，液-气相共存，焓和自由能）。许多重要的地球化学过程，如矿物沉积、变质作用和相分离的化学分馏作用，都是由含水地层流体的热力学行为控制的。不幸的是，大多数用于开发该系统EOS的实验数据都局限于比自然中遇到的PTX范围小得多的范围。为了克服数据可用性方面的这些重要限制，我们的研究方法将利用致密流体理论和分子模拟方法的最新进展：(1)支持构建EOS，该EOS不仅可以正确总结数据，还可以可靠地外推到PTX空间的所需区域（例如，深部地壳和岩浆条件）；(2)在分子水平上进行直接模拟，补充实验数据。提议的EOS将基于热力学摄动理论。在这种理论方法中，自由能被写成来自理想参照系和摄动修正的贡献之和。在提出的研究计划中，我们将集中精力开发最能代表所研究子系统行为的参考系统。我们的目标是降低表示测量行为所需的扰动修正的复杂性和幅度，以最大限度地提高EOS的外推特性。模型系统的分子动力学模拟将为测试参考系统的改进和混合规则提供有用的工具。为了正确描述临界区域的热力学性质，需要特殊的函数行为（标度行为）。我们将应用标度方法来改进临界区域预测，并研究如何将标度推广到计算其他热力学性质，如热含量和自由能。此外，我们将开发跨界EOS，它可以在关键区域内外提供准确的预测。为了在分子水平上通过模拟再现热力学性质，我们将继续开发模拟方法[例如，第一原理从头算（AIMD）和经典分子动力学（MD），吉布斯集合蒙特卡罗（GEMC）]。提出的研究的一个主要目的是通过开发溶液中离子的更好的分子间有效电位表示来显着提高离子溶液模拟的准确性。我们将在关键区域测试新方法，以提高GEMC方法和预测的性能。AIMD方法将用于指导分子间电位的发展，并研究系统性质（如局部极化）对这些相互作用的重要影响。这些方法将用于建立具有少量数据的系统的力，例如离子中性相互作用。

Weare and MollerEAR-0126331This research program will contribute the development of an equation of state (EOS), which can be used to accurately predict thermodynamic properties (e.g., liquid-vapor phase coexistence, enthalpy and free energy) in the NaCl-KCl-CaCl2-H2O-CO2-CH4 (SWG) system over the wide PTX ranges associated with Earth processes. Many important geochemical processes, such as mineral deposition, metamorphism and chemical fractionation via phase separation, are controlled by the thermodymanic behavior of aqueous formation fluids with compositions approximately in this system. Unfortunately, most experimental data available for development of an EOS for this system are confined to much smaller PTX ranges than those encountered in Nature. To overcome these important limitations in data availability, our research approach will use recent advances in the theory of dense fluids and molecular simulation methods to: (1) support the construction of an EOS that not only correctly summarizes data but also reliably extrapolates to desired regions of PTX space (e.g., deep crustal and magma conditions); and (2) supplement the experimental data by direct simulation at the molecular level. The proposed EOS will be based on thermodynamic perturbation theory. In this theoretical method the free energy is written as a sum of contributions from an ideal reference system and from a perturbation correction. In the proposed research program we will concentrate on developing reference systems that optimally represent the behavior of the subsystem under study. Our objective is to lower the complexity and magnitude of the perturbation corrections needed to represent the measured behavior in order to maximize the extrapolation properties of the EOS. Molecular dynamics simulations of model systems will provide useful tools for testing reference system improvements and mixing rules.Special functional behavior (scaling behavior) is required to correctly describe thermodynamic properties in the critical region. We will apply scaling methods to improve critical region predictions and examine how scaling can be generalized to calculate other thermodynamic properties, such as heat content and free energy. In addition, we will develop crossover EOS, which provide accurate predictions both in and away from the critical region. To reproduce thermodynamic properties via simulation at the molecular level, we will continue to develop simulation methods [e.g., first principles ab-initio (AIMD) and classical molecular dynamics (MD), Gibbs Ensemble Monte Carlo (GEMC)]. A main objective of the proposed research is to significantly improve the accuracy of ionic solution simulations by developing better intermolecular effective potential representations of ions in solution. We will test new methods to improve the performance of GEMC methods and prediction in the critical region. AIMD methods will be applied to guide intermolecular potential development and to study important effects on these interactions of system properties such as local polarization. These methods will be used to establish the forces for systems with little data, such as ion-neutral interactions.