熔融CaF_2的径向分布函数

RADIAL DISTRIBUTION FUNCTIONS OF MOLTEN CaF_2

熔融CaF_2是一种典型的离子液体,又是一种重要的冶金熔体.径向分布函数不仅是描述熔体结构的重要物理量,而且是计算熔体热力学性质的基础.实验上可以通过X 射线、中子衍射测得结构因子经Fourier 变换得到径向分布函数.已有使用X 射线衍射方法实验测定熔融CaF_2结构因子的报导.但由于实验上分解三种离子对Ca^(2+)-Ca^(2+),Ca^(2+)-F^-、F^--F^-偏结构因子的困难,未能给出相应的三种径向分布函数g++(r)、g+-(r)、g--(r)。

The coefficients b,ρ,and σ in Born-Mayer-Huggins potential were determinedempirically for three interactions in CaF_2 system.The potential suggested in this workhave reproduced the experimental lattice energy,bulk modulus,and three elasticconstant very well.The radial distribution functions for molten calcium fluoride havebeen given by molecular dynamics simulation with the potential obtained.The results show that there is a great deal of difference in the three radial distribution functions.The first peak of radial distribution function is very sharp in the cation-anion caseand smoothing down in the cation-cation and anion-anion case.The maximum of g_ _(r)distribution is not high and a limp point appears between the first peak and thefirst valley of g_ _(r)curve.The distances where the radial distribution function g+_(r)has a maximum are 2.25(?) for T=2000K and 2.21(?) for T=2200K.Thesevalues are less than 2.357(?),the distance between cation and anion in crystallinephase of calcium fluoride,that indicates there are some “holes” and chain-like struc-tures in molten system.