Helium diffusion in carbonate minerals is important for studying the physical and chemical properties and dynamic processes of Earth’s degassing. This paper discussed helium incorporation and diffusion mechanism in crystals of calcite and aragonite based on density functional theory calculations. The diffusion pathways, activation energies (E_a), and frequency factors (v) of helium under the surface and mantle condition were calculated. Calculations show an apperant anisotropy of helium diffusion in calcite, with more energetically favorable directions along a(b) axis. The moderate anisotropy of helium diffusion is showed in aragonite, in which the diffusion rate along c axis is slower than that along a axis. Under high pressure conditions, the activation energies of helium diffusion in aragonite increase with pressure. The closure temperature for calcite crystal varies from −54 ℃ to −25 ℃ in the direction [010], and for aragonite varies from −12 ℃ to 23 ℃ in [100]. Aragonite may be more retentive for helium than calcite under surface condition, which agrees well with previous experimental studies.

基于第一性原理分子动力学方法，计算了MgSiO3熔体在0~144 GPa、2 000~6 000 K的微观结构及其随压力、温度的变化特征。计算的近零压2 000 K下OSi、OMg和OO对分布函数的第一峰值位置分别为0.163 5、0.197 0和0.269 5 nm，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4.59 g/cm3时，原子间的平均键长随温度（小于5 000 K）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133 GPa、4 000 K条件下，MgSiO3熔体的OSi、OMg和OO平均键长分别为0.161 0、0.183 5和0.230 0 nm；从地表常压到核幔边界压力，平均SiO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。