A simple modeling method to extend first-principles electronic structure calculations to finite temperatures is presented. The method is applicable to crystalline solids exhibiting complex thermal disorder and employs quasi-harmonic models to represent the vibrational and magnetic free energy contributions. The main outcome is the Helmholtz free energy, calculated as a function of volume and temperature, from which the other related thermophysical properties (such as temperature-dependent lattice and elastic constants) can be derived. Our test calculations for Fe, Ni, Ti, and W metals in the paramagnetic state at temperatures of up to 1600 K show that the predictive capability of the quasi-harmonic modeling approach is mainly limited by the electron density functional approximation used and, in the second place, by the neglect of higher-order anharmonic effects. The developed methodology is equally applicable to disordered alloys and ordered compounds and can therefore be useful in modeling realistically complex materials.

中文翻译：

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金属热能的拟谐波模型

提出了一种将第一性原理电子结构计算扩展到有限温度的简单建模方法。该方法适用于表现出复杂热失调的结晶固体，并采用准谐波模型来表示振动和磁自由能的贡献。主要结果是根据体积和温度计算的亥姆霍兹自由能，从中可以推导出其他相关的热物理性质（例如与温度有关的晶格和弹性常数）。我们在高达1600 K的温度下对顺磁性状态下的Fe，Ni，Ti和W金属的测试计算表明，准谐波建模方法的预测能力主要受所用电子密度函数近似的限制，并且在第二个地方，被高阶非谐效应所忽略。所开发的方法学同样适用于无序合金和有序化合物，因此可用于对实际复杂的材料进行建模。