First-Principles Calculation of Ternary Phase Diagrams

采用合金相稳定性的第一性原理电子理论研究了二元和三元体系的热力学性质和温度-组成相图。本研究的重点是基于结合能、振动熵和构型熵的量子力学计算的计算方案的开发和测试，以预测固态相的稳定性。利用线性松饼-锡轨道和局部密度近似进行了有序化合物总能量的电子结构计算。利用Liner Muffin-Tin轨道总能量计算得到了构型有序化合物的多原子有效化学相互作用、平衡晶格常数、体模量、Debye温度、Gruneisen常数和膨胀系数。这些计算为平衡相图的计算提供了所有必要的信息。三元平衡和亚稳相图将计算一些重要的铝化物，以建立可能提供预测结果的趋势。精确合金相图的计算通常基于实验输入和现象学模型。所得的相图有时缺乏预测能力。本文提出的研究将基于第一性原理计算相图；本质上只提供构成合金的原子的性质。第一性原理相图的计算是设计具有理想性能的新材料的重要步骤。目前的工作将发展技术来做这些计算更困难的三元合金的情况。

A first-principles electronic theory of alloy phase stability is used to investigate the thermodynamic properties and the temperature-composition phase diagrams of binary and ternary systems. The emphasis of this study is on the development and testing of computational schemes - based on quantum mechanical calculations of binding energies, vibrational entropies and configurational entropies - in order to predict solid state phase stability. Electronic structure calculations of the total energy of ordered compounds are carried out using the Linear Muffin-Tin Orbital and the Local Density Approximations. The Liner Muffin-Tin Orbitals total energy calculations are used to obtain multiatom effective chemical interactions, equilibrium lattice constants, bulk moduli, Debye temperatures, Gruneisen Constants and expansion coefficients of configurationally ordered compounds. These calculations provide all information necessary for the computation of equilibrium phase diagrams. Ternary equilibrium and metastable phase diagrams will be calculated for a number of important alumindes to establish trends which may offer predictive results. %%% Calculations of accurate alloy phase diagrams have usually been based on experimental input and phenomenological models. The resulting phase diagrams were sometimes lacking in predictive capability. The research proposed here will calculate phase diagrams based on first-principles; essentially providing only the properties of the atoms making up the alloy. The calculation of first-principles phase diagrams is an important step in the design of new materials having desired properties. The present work will develop techniques to do these calculations for the more difficult case of ternary alloys.