2013年9月，第19卷，第3期，456-462页 September 2013,Vol.19,No.3,p.456462
高校地质学报
Geological Journal of China Universities
熔融SiO,中原子自扩散性质的分子动力学模拟
孙义程，周会群，尹坤，黄倩，徐士进
南京大学地球科学与工程学院，南京210093
摘要：研究地慢熔体中元索的扩散性质有着重要的意义，因其影响着元素的交换和分馏过程。SiO,作为地慢组成的重要组分之一，其物理化学行为对于地慢动力学过程有着重要的意义。本文研究了SiO,熔体中元素的扩散机制和自扩散系数与压力的关系，采用Marsestrelch势场对含有4500个原子的熔融SiO,体系进行了分子动力学模拟，计算了硅氧自扩散系数在 3000K温度下随压力的变化。模拟结果显示，在0.0001~40GPa的压力区间，硅氧元素的自扩散系数均先上升后下降，在 17.5CPa时达到最大值，0原子的扩散速率略高于Si原子。硅氧元索的扩散方式为缺陷控制运移机制，其中硅原子的五配位结构的形成是关键，为导致扩散系数随压力增大而上升的主要原因，扩散系数的最大值意味着SiO，熔体中5配位硅形成机
制的改变。本文也计算了单位［SiO，］的平均体积和压力的关系，结果与实验很吻合。关键调：Morsestretch势场；自扩散系数；SiO,；分子动力学
中图分类号：P594
文献标识码：A
文章编号：10067493（2013）0345607
MolecularDynamicsStudyofSelf-DiffusionofSilicaand
OxygeninSilicaMelt
SUNYicheng,ZHOUHuiqun,YINKun,HUANGQian,XUShijin School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China
Abstract: The diffusivity of elements in mineral controls the processes of ion exchange, isotope fractionation, and phase transition. As one of the most important components of silicate melts, SiO, plays a very important role in the earth mantle structure and the dynamics process. This paper focuses on the ion diffusion mechanism in silica melt and the corresponding pressure when the self-diffusion coefficient reaches its maximum value, We calculated the changing process of Si and O ions' self-diffusion coefficient at temperatures of 3000 K by using the molecular dynamics (MD) simulation which contains 4500 ions in the silica melt with Morse stretch potential. Calculations show that both Si and O self-diffusion coefficients increase at initial compression and reach maximum values at 17.5 GPa. Self-diffusion coefficients for O are slightly greater than that for Si. The Si and O ions diffusion feature is caused by a defect-controlled transport mechanism and the five-fold coordination structure of Si ion is the main reason for the rise of the diffusion coefficients in aceord with the increasing pressure. The fact that the diffusion coefficient reaches its maximum value means the change in the formation of five-fold Si in the liquid silica. This paper also calculated the relationship between the average volume of [SiO,] unit and the pressure, which agrees well with the results of our experiment.
Key words: morse stretch potential; self-diffusion coefficient; SiO; molecular dynamics First author: SUN Yicheng, Master student; E-mail: sunyichengoo1@sina.com
收稿日期：20120427；修回日期：20120613 基金项目：国家自然科学基金项目（40973003）
作者简介：孙义程，男，1987年生，硕士，主要从事矿物物理方需的研究；E-mail:sunyicheng001@sina.no