Efficient calculation of temperature dependence of solid-phase free energies by overlap sampling coupled with harmonically targeted perturbation.
Efficient calculation of temperature dependence of solid-phase free energies by overlap sampling coupled with harmonically targeted perturbation.
复制标题
通过重叠采样与谐波目标扰动相结合，有效计算固相自由能的温度依赖性。
DOI：
10.1063/1.3483899
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
D. Kofke
中科院分区：
文献类型：
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作者：
T. B. Tan;A. Schultz;D. Kofke
本文研究了一种计算结晶固体自由能随温度变化的方法。在该方法中，通过班尼特最优化的双采样自由能微扰计算附近温度之间的自由能差。与此相耦合的是一种谐波目标扰动，它以与温度变化一致的方式移动原子，这样对于谐波系统，自由能差将被毫无误差地恢复。一系列这样的扰动可以组合起来，以弥合更大的温度差距。我们通过应用于反幂次软势u（r）=ε（σ/r）（n），在直到熔化条件的温度范围内测试这种谐波目标温度扰动（HTTP）方法。三个指数值（n=12，9，和6）的潜力进行了研究与不同的晶体结构，特别是面心立方（fcc），体心立方（bcc），和六方密堆积。每个系统的绝对自由能（仅经典）通过将该系列实现到接近零的温度来获得，其中谐波模型变得非常准确。HTTP方法显示出提供非常精确的结果，自由能的误差小于10（5）的两部分。在无限系统极限的各种结构的热力学稳定性的分析证实了以前的研究结果。特别地，对于n=12和9，fcc结构对于直到熔化的所有温度都是稳定的，并且对于n=6，bcc晶体对于高于kT/ε=0.802±0.001的温度变得相对于fcc稳定。在分析中不考虑空位和其他缺陷的影响。
We examine a method for computing the change in free energy with temperature of a crystalline solid. In the method, the free-energy difference between nearby temperatures is calculated via overlap-sampling free-energy perturbation with Bennett's optimization. Coupled to this is a harmonically targeted perturbation that displaces the atoms in a manner consistent with the temperature change, such that for a harmonic system, the free-energy difference would be recovered with no error. A series of such perturbations can be assembled to bridge larger gaps in temperature. We test this harmonically targeted temperature perturbation (HTTP) method through the application to the inverse-power soft potential, u(r)=ε(σ/r)(n), over a range of temperatures up to the melting condition. Three exponent values (n=12, 9, and 6) for the potential are studied with different crystal structures, specifically face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close packing. Absolute free energies (classical only) for each system are obtained by implementing the series to near-zero temperature, where the harmonic model becomes very accurate. The HTTP method is shown to provide very precise results, with errors in the free energy smaller than two parts in 10(5). An analysis of the thermodynamic stability of the various structures in the infinite-system limit confirms previous findings. In particular, for n=12 and 9, the fcc structure is stable for all temperatures up to melting, and for n=6, the bcc crystal becomes stable relative to fcc for temperatures above kT/ε=0.802±0.001. The effects of vacancies and other defects are not considered in the analysis.