金属Nb的Finnis-Sinclair势开发及势函数形式对材料性能的影响

Development of Finnis-Sinclair potential of metal Nb and the influence of potential function form on the properties of material

对于计算材料科学的研究者来说,经常由于找不到合适的原子间势而工作受阻.本文将在Finnis-Sinclair势的框架下,通过开发金属Nb的Finnis-Sinclair势而给出较详细的原子间势拟合、检验、修正的过程.首先建立原子间势与材料宏观性能之间的关系,然后通过再现金属Nb的结合能、体模量、表面能、空位形成能及平衡点阵常数的实验数据的方法拟合金属Nb的Finnis-Sinclair势.利用所构建的原子间势计算金属Nb的弹性常数、剪切模量及柯西压力来检验势函数.讨论势函数曲线形状对间隙形成能的影响,进而根据间隙能的计算数据修正已构建的原子间势.讨论截断距离的处理方法.本文的结果一方面为构建原子间势函数库提供资料,为构建与Nb相关的合金原子间势奠定基础;另一方面,为开发和改善原子间势质量提供方法和依据.

Researchers’work on computational materials is often hampered by the lack of suitable intera tomic potentials.In this paper,under the framework of Finnis-Sinclair(FS)potentials,the process of fitting,testing and correction of interatomic potential is given in detail by developing the FS potential for metal Nb.First,the relationship between the interatomic potential and the macroscopic properties of the material is established.Then,the Finnis-Sinclair potential of metal Nb is fitted by reproducing the experimental data,such as the cohesive energy,bulk modulus,surface energy,vacancy formation energy and equilibrium lattice constant,and the fitting mean square error is less than 10–7.In order to test the interatomic potential,the elastic constant,shear modulus and Cauchy pressure of metal Nb are calculated by the constructed interatomic potential.In addition,how the form of the interatomic potential function affects the interstitial performance is discussed,and the constructed interatomic potential is modified according to the results of density functional theory(DFT)of the interstitial formation energy.The treatment of cutoff distance is also discussed.In the paper,the results are as follows.1)The original form of FS potential is not suitable for extending the atomic interaction to the third nearest neighbor.Through analysis and test,it is found that when the modified electron density function is in the form of the fourth power and the form of the pair potential function is in the form of the sixth power polynomial,the interatomic potential can better describe the interatomic interaction;2)The result of interstitial formation energy is taken as the target value to modify the behavior of the pair potential function in the near distance,and the modified interatomic potential gives the interstitial formation energy close to the result of DFT.When the interstitial energy calculated by the interatomic potential is larger than the target value,the pair potential curve of near distance will be softened by the superposition of a polynomial term,otherwise,the pair potential curve will be stiffened;3)When the physical quantity under equilibrium state is used as the fitting data,the fitted potential parameters and the elastic constant results will not be affected,while adjusting the curve form of the potential function,as long as none of the function value,the slope and the curvature of the function curve is changed at each neighbor position.The magnitude of interstitial energy will be affected by changing the shape of the curve that is less than the first neighbor range;4)Under the cutoff strategy in this paper,changing the cutoff distance has almost no influence on the calculated results of potential parameters or crystal properties,but has a slight influence on the mean square error of the fitting results.The results of this paper provide some information for the construction of interatomic potentials database,and lay a foundation for constructing the Nb-related interatomic potential of alloy.And it also provides a method and basis for developing and improving the quality of interatomic potential.