Computer simulation of the structural and physical properties of silicate crystals and melts at high temperatures and high pressures

Na_2O-CaO-MgO-Al_2O_3-SiO_2(NCMAS)系统中的晶体和熔体是地壳和地幔的重要组成部分。分子动力学(MD)和晶格动力学(LD)方法用于计算晶体的性质，而分子动力学技术用于模拟熔体。离子间相互作用势被认为是两两相加的库仑、范德华吸引和排斥相互作用的总和。此外，为了考虑晶体和熔体中的多体作用力，建立了呼吸壳模型进行模拟，该模型允许0离子的排斥半径在其他离子的作用下各向同性地变形。离子的净电荷被限制为2q(Na)=q(Ca)=q(Mg)=2/3q(A1)=1/2q(Si)=-q(0)，以在NCMAS系统中对晶体和熔体施加电势。所需的能量参数，包括氧电荷、排斥半径、离子的范德华系数和氧气呼吸参数，被经验地推导出来，以再现观察到的广泛结构的温度-压力-体积(T-P-V)状态方程。NCMAS系统中的各种晶体，以及在高温下测得的顽辉石、硅灰石、透辉石、钠长石和钙长石熔体的体积。尽管研究了各种各样的晶体和熔体，但LD和MD模拟在NCMAS系统中准确地再现了晶体和熔体的测量结构和物理性质是相当成功的。

Crystals and melts in the Na_2O-CaO-MgO-Al_2O_3-SiO_2 (NCMAS) system are important components of the earth's crust and mantle. Both molecular dynamics (MD) and lattice dynamics (LD) methods are used to calculate the properties of crystals, while the MD technique is applied to simulate melts. The interionic potential is taken to be the sum of pairwise additive Coulomb, van der Waals attraction, and repulsive interactions. In addition, in order to take account of many-body forces in crystals and melts, the breathing shell model is developed for simulation, in which the repulsive radii of 0 ions are allowed to deform isotropically under the effects of other ions in the system concerned. The net charges of the ions are constrained to be 2q(Na)=q(Ca)=q(Mg)=2/3q(A1)=1/2q(Si)=-q(0) to apply the potential to both crystals and melts with any composition in the NCMAS system. Required energy parameters, including the oxygen charge, repulsive radii, van der Waals coefficients of ions, and the oxygen breathing parameters, were derived empirically to reproduce the observed temperature-pressure-volume (T-P-V) equations of state of a wide structural. variety of crystals in the NCMAS system, as well as the measured volumes of enstatite, wollastonite, diopside, albite, and anorthite melts at high temperatures. In spite of a wide variety of crystals and melts studied, the LD and MD simulations are quite successful in reproducing accurately the measured structural and physical properties of both crystals and melts in the NCMAS system.