Observation and Simulation of atomic motion in the Eath internal materials

本文讨论了扩展X射线吸收精细结构（EXAFS）谱和衍射方法在振动动力学研究中的应用。我们的研究探索了EXAFS和衍射实验提供一个有效的原子间势和一个有效的绝热单粒子势与温度无关的形状，分别从每个Debye-Waller因子的可能性。EXAFS方法已被用于分子动力学模拟中原子间相互作用势的可靠性检验。原子间相互作用势的可靠表示对于更好地理解地球内部物质的热性质具有重要意义. EXAFS和衍射方法揭示了地幔中许多物质如镁铝榴石、镁氧方铁矿、MgSiO_3钙钛矿、Mg_2SiO_4尖晶石和方石英的精确晶体结构和热性质.在势参数拟合中，我们直接对EXAFS函数进行了数值积分，计算了非谐有效对势。通过计算动力学矩阵，利用势参数估计了声子能量。Gruneisen参数也从获得的参数值计算。原子对的振动运动依赖于晶格类型和化学键。材料的振动特性不仅受压力的影响，而且受配位数的影响。相变点处配位数的变化对有效对势的影响很大。配位数较高的高压相比配位数较低的低压相具有更宽的有效对势。从有效对电势和阴阳离子间距分布两个方面讨论了金属离子的导电机理。强相关位移可归因于局部相互作用的共价键。

The usefulness of Extended X-ray absorption fine structure (EXAFS) spectroscopy arid diffraction method in studying vibration dynamics has been discussed by this study. Our studies have explored the possibility that EXAFS and diffraction experiments provide an effective interatomic potential and an effective adiabatic one-particle potential with temperaturew-independent shape, respectively, from each Debye-Waller factor. EXAFS method has been utilized as a reliability test for the interatomic potentials in molecular dynamics simulation. Reliable representation of interatomic potential is important for better understanding the thermal properties of the Earth intrenal materials.Precise crystal structure and thermal properties in many materials in the Earth's mantle such as majorite garnet, magnesia wustite, MgSiO3 perovskite, Mg2SiO4 spinel and stishovite heve been revealed by the EXAFS and diffraction method. In the potential parameter fitting, we have directly carried out the numerical integration of the EXAFS function and evaluated the anharmonic effective pair potential. The phonon energies have been estimated using the potential parameter by calculating the dynamical matrix. The Gruneisen parameter is also calculated from the obtained parameter values. The vibrational motion of pair of atoms depend on the lattice type and chemical bonding. Vibrational properties in materials is influenced not only by pressure but also by coordination number The effective pair potential is affected largely by the change in coordination number at a phase transition point.. High pressure phase with higher coordination number has broader effective pair potential than low pressure phase with lower coordination number. Ionic conduction mechanism in menerals has been discussed based on the effective pair potential and distribution of cation-anion distances. The strongly correlated displacement can be attributed to covalent bonds which interact locally.