This work proposes an efficient and accurate methodology of ab initio thermodynamics to predict phase diagrams of III–V pseudobinary systems. The innumerable configurations of solid solutions are efficiently considered while maintaining accuracy by calculating the energies of freely relaxed configurations with the combined methodology using density functional theory calculations and cluster expansion. Then, the thermodynamic properties are calculated following a grand canonical ensemble framework that takes into account the local compositional fluctuation. The local strain energy induced by this local compositional fluctuation is found to be independent of the configuration; hence, it is calculated separately and added to the energy of a freely relaxed configuration, which significantly reduces the computational cost. This novel methodology is applied to calculate the phase diagrams of Ga(As,Sb) and (In,Ga)As, showing a good agreement with previous experimental reports. Notably, the strain energy is indispensable to predict phase diagrams accurately. It implies both the validity and the applicability of this method to other III–V pseudobinary systems. From an understanding of the crucial role of the strain energy in phase separation, an intuitive prediction is suggested through a simple estimation of the strain energy using the ratio of lattice parameters between various III–V semiconductor materials.

这项工作提出了一种从头开始的有效而准确的方法热力学来预测III–V伪二元系统的相图。通过使用密度泛函理论计算和簇扩展的组合方法计算自由松弛构型的能量，可以有效地考虑无数种固溶体的构型，同时保持精度。然后，在考虑到局部成分波动的大正则整体框架下计算热力学性质。发现由这种局部组成波动引起的局部应变能与构型无关。因此，它是单独计算的，并添加到自由松弛配置的能量中，从而显着降低了计算成本。这种新颖的方法论被用于计算Ga（As，Sb）和（In，Ga）As的相图，与先前的实验报告显示出良好的一致性。值得注意的是，应变能对于准确预测相图必不可少。它暗示了该方法对其他III–V伪二进制系统的有效性和适用性。通过了解应变能在相分离中的关键作用，可以通过使用各种III–V半导体材料之间的晶格参数比率对应变能进行简单估算来提出直观的预测。