Elastic constants of random solid solutions by SQS and CPA approaches: the case of fcc Ti-Al
Elastic constants of random solid solutions by SQS and CPA approaches: the case of fcc Ti-Al
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DOI：
10.1088/0953-8984/27/31/315702
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发表时间：
2015-07
期刊：
影响因子：
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通讯作者：
Li-Yun Tian;Q. Hu;Rui Yang;Jijun Zhao;B. Johansson;L. Vitos
中科院分区：
文献类型：
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作者：
Li-Yun Tian;Q. Hu;Rui Yang;Jijun Zhao;B. Johansson;L. Vitos
特殊准随机结构(SQS)和相干势近似(CPA)是随机合金第一性原理计算中广泛采用的两种方法。在这里，我们通过关注局域晶格失真(LLD)和晶体对称性效应来仔细研究这些方法。以面心立方(Fcc)Ti1−xAlx(0⩽x⩽1？>；)合金为例，比较了面心立方(Fcc)Ti1xAlx(0？)对于CPA和SQS计算，我们分别采用了维也纳从头算模拟程序(VASP)中实现的精确Muffin-tin轨道(EMTO)方法和赝势方法。结果表明，VASP-SQS和EMTO-CPA参数对组成的预测趋势是一致的。与激光二极管相关的能量随着x的增加而增加，直到x=0.625∼0.750？gt；之后急剧下降。LLD对晶格常数和C12弹性常数的影响可以忽略不计。具有较大LLD的合金在原子弛豫后C11和C44降低，但对C11和C44的变化趋势影响不大。总体而言，与对称性降低相关的弹性参数的不确定性要优于两种技术之间的差异，包括LLD的影响。
Special quasi-random structure (SQS) and coherent potential approximation (CPA) are techniques widely employed in the first-principles calculations of random alloys. Here we scrutinize these approaches by focusing on the local lattice distortion (LLD) and the crystal symmetry effects. We compare the elastic parameters obtained from SQS and CPA calculations, taking the random face-centered cubic (fcc) Ti1−xAlx (0⩽x⩽1 ?>) alloy as an example of systems with components showing different electronic structures and bonding characteristics. For the CPA and SQS calculations, we employ the Exact Muffin-Tin Orbitals (EMTO) method and the pseudopotential method as implemented in the Vienna Ab initio Simulation Package (VASP), respectively. We show that the predicted trends of the VASP-SQS and EMTO-CPA parameters against composition are in good agreement with each other. The energy associated with the LLD increases with x up to x=0.625∼0.750 ?> and drops drastically thereafter. The influence of the LLD on the lattice constants and C12 elastic constant is negligible. C11 and C44 decrease after atomic relaxation for alloys with large LLD, however, the trends of C11 and C44 are not significantly affected. In general, the uncertainties in the elastic parameters associated with the symmetry lowering turn out to be superior to the differences between the two techniques including the effect of LLD.