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高温高压下MgSiO3熔体结构的第一性原理分子动力学研究

DOI: 10.11858/gywlxb.2014.03.003, PP. 273-282

Keywords: MgSiO3熔体,第一性原理分子动力学,对分布函数,平均配位数

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Abstract:

基于第一性原理分子动力学方法,计算了MgSiO3熔体在0~144GPa、2000~6000K的微观结构及其随压力、温度的变化特征。计算的近零压2000K下O—Si、O—Mg和O—O对分布函数的第一峰值位置分别为0.1635、0.1970和0.2695nm,与实验结果吻合很好。随着压力和温度的变化,MgSiO3熔体结构发生了显著变化,尤其是随着压力增加,结构变得更致密;当密度为4.59g/cm3时,原子间的平均键长随温度(小于5000K)增加而减小,在常压和更高的压力下,原子间的平均键长随温度变化不明显。在133GPa、4000K条件下,MgSiO3熔体的O—Si、O—Mg和O—O平均键长分别为0.1610、0.1835和0.2300nm;从地表常压到核幔边界压力,平均Si—O配位数从4变到6,桥氧数目比例由31.3%增高到72.9%。MgSiO3熔体微观结构的认识对了解地幔内硅酸盐流体性质及其对地幔动力学的影响有重要意义。

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