摘要
导出一组对铬铁矿及其高压相、分解产物都适用的Buckingham势能参数，用于铬铁矿高压相变、分解以及高压相卸压降温过程的分子动力学模拟．首先，利用密度泛函理论（DFT）计算获得铬铁矿、钙铁相、钙钛相、FeO和Cr2O3不同体积时的结构和总能量．再根据晶格能与总能量之间的关系，由DFT所得结构和总能量，列出势能参数所满足方程组．应用遗传算法这一全局优化算法获得势能参数．为检验所得势能参数的正确性，将其用于分子动力学计算，得出的5种晶体的晶格常数与实验和DFT结果分别差～2％和～1％，得出的5种晶体的V（p）关系与DFT拟合的状态方程曲线相吻合．
Chen et al （2003, Geochimica et Cosmochimica, 67： 3 937-3 942） have discovered the first natural occurrences of two high-pressure polymorphs of chromite spinel in the shock-metamorphosed Suizhou meteorite. Synchrotron X-ray diffraction analysis reveals that one has a calcium-ferrite （CaFe2O4 ） structure with Pnma space group and the other has a calcium-titanium （CaTi2O4 ） structure with Cmcrn space group. Considering the ubiquitous presence of chromite, the spinel-CaFe2O4-CaTi2O4 transition series could potentially provide a comprehensive pressure gauge system.
Molecular dynamics is currently a feasible method in simulating phenomena, such as phase transitions, under high pressure and temperature. Because the plase transitions possibly take place between chromite, CaFe2O4-phase, CaTi2O4-phase and potentially FeO and Cr2O3, it is necessary to determine an empirical potential function that can accurately describe each of the five crystals in the molecular dynamics simulation.
Because the published experimental data of chromite and its two high-pressure phases are rare and incomplete, we derived the transferable force field by fitting Buckingham potential function to the data obtained from DFT calculations of the five crystals. The density functional theory （DFT） caculation is performed by using the PWscf codes that use plane-wave pseudopotential method based on the DFT. For each crystal we calculated the optimized atomic structure and the corresponding total energy under each different cell volume. We assumed that such total energy can be divided into lattice energy and the total sum of the energy of free ions after the crystal is separated apart. While the former can be computed by the GULP codes from the set of potential parameters to be fitted combined with the already calculated atomic structure, the latter is unknown. We have one equation about these parameters for each different volume of each crystal. The set of potential parameters of interest is just the solution of the system of eq
出处
《南京大学学报（自然科学版）》
CAS
CSCD
北大核心
2007年第5期520-525,共6页
Journal of Nanjing University（Natural Science）
基金
国家自然科学基金(40472029)
关键词
铬铁矿
分子动力学
势能参数
密度泛函理论
遗传算法
chromite, molecular dynamics, potential parameter, density founctional theory（DFT）, genetics algorithm
