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Theoretical and Experimental Exploration of the Energy Landscape of LiI

机译:刘能源景观的理论与实验探索

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The prediction of the existence and stability of (meta)-stable phases in a chemical systen is realized via a two-step process: identification of structure candidates through global exploration of the classical empirical energy landscape, followed by a local optimization of the candidates on ab-initio level employing a heuristic algorithm. From the computed energy/volume curves, one can then calculate the thermodynamically stable phase at a given pressure and the transition pressures among the phases. In order to gain insight into the kinetic stability of the structure candidates, one computes estimates of the energy and enthalpy barriers around the structures with the so-called threshold algorithm, yielding a tree graph representation of the chemical system. In this work we perform a theoretical and experimental study of the LiI energy landscape. We determine the structure candidates, construct the tree graph representation and compute the ab-initio energy/volume curves for the hypothetical structures. We find that the thermodynamically preferred modifications at standard pressure should exhibit the rock salt and the wurtzite structure, respectively. In order to validate our predictions by experiments, we have employed the newly developed 'Low-Temperature -Atomic Beam Deposition' (LT-ABD) technique, which allows to disperse the components of the desired product at an atomic level and in an appropriate ratio. After depositing LiI at T = 77 K, the first crystallization occurs at T ≈ 173 K in the wurtzite-type structure followed by a transition to the more stable rock salt-type structure at T ≈ 273 K. At room temperature only the cubic phase remains.
机译:通过两步过程实现了化学系统中(Meta)-stable阶段的存在和稳定性的预测:通过全球探索经典经验能量景观的结构识别,其次是候选人的局部优化采用启发式算法的AB-Initio级别。从计算的能量/体积曲线,然后可以在给定的压力下计算热力学稳定的相位和相之间的过渡压力。为了能够深入了解结构候选的动力学稳定性,通过所谓的阈值算法计算围绕结构的能量和焓障碍的估计,从而产生化学系统的树形图。在这项工作中,我们对Lii能量景观进行了理论和实验研究。我们确定结构候选,构造树图表示,并计算假设结构的AB-Initio能量/体积曲线。我们发现标准压力下的热力学优选的修饰分别应分别显示岩盐和紫立岩结构。为了通过实验验证我们的预测,我们采用了新开发的“低温 - 射线束沉积”(LT-ABD)技术,其允许以原子水平和适当的比例将所需产物的组分分散。在T = 77k沉积LiI之后,在纯钛矿型结构中在T≈173k中发生第一结晶,然后在T≈273k的岩盐型结构中过渡到≈273k.在室温下仅间隔遗迹。

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