Discerning Chemical Pressure amidst Weak Potentials: Vibrational Modes and Dumbbell/Atom Substitution in Intermetallic Aluminides
Discerning Chemical Pressure amidst Weak Potentials: Vibrational Modes and Dumbbell/Atom Substitution in Intermetallic Aluminides
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DOI：
10.1021/acs.jpca.8b07419
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发表时间：
2018-10-25
影响因子：
2.9
通讯作者：
Fredrickson, Daniel C.
中科院分区：
文献类型：
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作者：
Hilleke, Katerina P.;Fredrickson, Daniel C.
原子的空间要求通常被认为是化学系统的结构、反应性和物理性质的关键约束。然而，这种考虑的经验性质使得用第一性原理计算来阐明这些尺寸效应具有挑战性。 DFT 化学压力 (DFT-CP) 分析是一种提取原子尺寸在材料晶体结构中的作用的有效方法，其中 DFT 计算的输出用于构建由于晶格约束而作用于原子之间的局部压力图。虽然原则上该方法应该适用于 DFT 被认为是适当处理的任何系统，但到目前为止，当半核电子包含在每个原子的价集中以提供对压缩的显式排斥响应时，该方法最为成功。在本文中，我们解决了这个限制因素，使用基于铝的金属间化合物作为模型系统，铝是许多结构有趣的相中的关键成分，不适合用半核赝势进行建模。从 Laves 相 CaAl2 开始，我们说明了由于 Al 原子上的核心响应最小，用原始方法创建反映化合物声子能带结构的 CP 方案的困难。这些缺陷通过三个能量项的空间映射得到解决，这三个能量项以前被视为同质背景效应：Ewald、E-alpha 和非局域赝势分量。当电荷转移被考虑到积分方案中时，无论 Ca 是用半核赝势还是纯价赝势建模，CaAl2 都可以获得与声子能带结构一致的 CP 方案。最后，我们通过将修改后的方法应用于 La3Al11 结构来证明其实用性，该结构通过用单个 Al 原子取代选定的 Al-2 对来缓解假设的 BaAl4 型母相中可能遇到的 CP。然后 La3Al11 作为一个更普遍现象的例子出现，即 CP 驱动的简单图案替换。
The space requirements of atoms are generally regarded as key constraints in the structures, reactivity, and physical properties of chemical systems. However, the empirical nature of such considerations renders the elucidation of these size effects with first-principles calculations challenging. DFT-chemical pressure (DFT-CP) analysis, in which the output of DFT calculations is used to construct maps of the local pressures acting between atoms due to lattice constraints, is one productive approach to extracting the role of atomic size in the crystal structures of materials. While in principle this method should be applicable to any system for which DFT is deemed an appropriate treatment, so far it has worked most successfully when semicore electrons are included in the valence set of each atom to supply an explicit repulsive response to compression. In this Article, we address this limiting factor, using as model systems intermetallics based on aluminum, a key component in many structurally interesting phases that is not amenable to modeling with a semicore pseudopotential. Beginning with the Laves phase CaAl2, we illustrate the difficulties of creating a CP scheme that reflects the compound's phonon band structure with the original method due to minimal core responses on the Al atoms. These deficiencies are resolved through a spatial mapping of three energetic terms that were previously treated as homogeneous background effects: the Ewald, E-alpha, and nonlocal pseudopotential components. When charge transfer is factored into the integration scheme, CP schemes consistent with the phonon band structure are obtainable for CaAl2, regardless of whether Ca is modeled with a semicore or valence-only pseudopotential. Finally, we demonstrate the utility of the revised method through its application to the La3Al11 structure, which is shown to soothe CPs that would be encountered in a hypothetical BaAl4 -type parent phase through the substitution of selected Al-2 pairs with single Al atoms. La3Al11 then emerges as an example of a more general phenomenon, CP-driven substitutions of simple motifs.