用第一性原理解释能量不稳定晶体结构的熵驱动稳定化
Entropy driven stabilization of energetically unstable crystal structures explained from first principles theory
摘要：
计算晶体热力学的传统方法评估谐波声子谱，因此在谐波近似下晶体结构不稳定的常见和重要情况下不起作用，例如体心立方（bcc）晶体结构，当它作为许多金属的高温相出现时。为了解决这个问题，从第一性原理出发，发展了一种自洽计算温度相关声子谱的方法。该方法结合了玻恩的原子间自洽声子方法的概念与超级细胞中精确的原子间力的第一性原理计算。该方法已被测试的高温bcc相的Ti，Zr和Hf，作为代表性的例子，并发现重现所观察到的高温声子频率具有良好的精度。
英文摘要：
Conventional methods to calculate the thermodynamics of crystals evaluate the harmonic phonon spectra and therefore do not work in frequent and important situations where the crystal structure is unstable in the harmonic approximation, such as the body-centered cubic (bcc) crystal structure when it appears as a high-temperature phase of many metals. A method for calculating temperature dependent phonon spectra self consistently from first principles has been developed to address this issue. The method combines concepts from Born's inter-atomic self-consistent phonon approach with first principles calculations of accurate inter-atomic forces in a super-cell. The method has been tested on the high temperature bcc phase of Ti, Zr and Hf, as representative examples, and is found to reproduce the observed high temperature phonon frequencies with good accuracy.
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