Ab Initio Two-Phase Molecular Dynamics on the Melting Curve of SiO2

• Published in: Journal of earth science (Wuhan, China) Vol. 21; no. 5; pp. 801 - 810
• Main Authors: Usui, Yusuke, Tsuchiya, Taku
• Format: Journal Article
• Language: English
• Published: China University of Geosciences China University of Geosciences 01.10.2010; Springer Nature B.V
• Subjects: Biogeosciences; Diffusion coefficient; Earth and Environmental Science; Earth science; Earth Sciences; Geochemistry; Geology; Geotechnical Engineering & Applied Earth Sciences; Melting; Molecular biology; Silica; Simulation; SiO2; Temperature effects; 分子动力学模拟; 核幔边界; 熔化曲线; 熔化温度; 自扩散系数; 运输性能; 面向对象; Melting Curve; Mean Square Displacement; Lower Mantle; Eutectic Phase Diagram; Eutectic Temperature
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-010-0126-9

Ab initio two-phase molecular dynamics simulations were performed on silica at pressures of 20-160 GPa and temperatures of 2 500-6 000 K to examine its solid-liquid phase boundary. Results indicate a melting temperature （Tin） of 5 900 K at 135 GPa. This is 1 100 K higher than the temperature considered for the core-mantle boundary （CMB） of about 3 800 K. The calculated melting temperature is fairly consistent with classical MD （molecular dynamics） simulations. For liquid silica, the O-O coordination number is found to be 12 along the Tm and is almost unchanged with increasing pressure. The self-diffusion coefficients of O and Si atoms are determined to be 1.3×10^-9-3.3×10^-9 m2/s, and the viscosity is 0.02-0.03 Pa＇s along the Tin. We find that these transport properties depend less on pressure in the wide range up of more than 135 GPa. The eutectic temperatures in the MgO-SiO2 systems were evaluated and found to be 700 K higher than the CMB temperature, though they would decrease considerably in more realistic mantle compositions.