固溶合金第一性原理计算方法初探

A PRIMARY STUDY ON THE FIRST-PRINCIPLES CALCULATION METHOD FOR SOLID SOLUTION ALLOY

固溶合金第一性原理计算在新型合金物性研究与合金组分优化设计中扮演着重要角色.固溶合金具有化学无序结构,晶格平移对称性破缺.难以直接应用标准的第一性原理计算方法.本文介绍了确定组分固溶合金第一性原理计算的主要两类方法.第一类方法是相干势近似方法,我们推导了相干势近似的自洽方程.基于多重散射理论梳理了单格点杂质系统Green函数的计算方法.第二类方法是超胞结构建模方法,我们介绍了相似原子环境的数学模型,推导了整体化学无序与短程化学有序的统一描述方法,证明了两种超胞结构建模方法最优解之间的关系.结合第一性原理计算与热力学模型,我们应用这两类方法预测了变组分铀铌合金的晶格参数与典型镁铝合金的热力学物性.获得了实验验证.

First-principles calculations of solid solution alloy play an important role in property study and optimal design of new alloys.The solid solution alloy is in chemical disorder with translation symmetry broken,which raises difficulty in using directly conventional first-principles approaches.In this paper,we discuss two first-principles methods for the solid solution alloy with given concentration.The first is the coherent potential approximation(CPA).We derive the self-consistent equation of CPA,and revisit the computational scheme for the Green function of the single impurity system.The second method is based on the supercell modeling.We introduce the mathematical model of the similar atomic environment(SAE) and the unified description of chemical disorder with short-range order.And we prove the relationship between the optimal solutions of two modeling methods.Combined with first-principles calculations and thermodynamic models,we apply the two methods to predict the lattice structures of U-Nb alloys with varying concentration and thermodynamic properties of one typical Mg-Al alloy,which is verified by comparing with the experiment results.