Development of a variational APW method with its application to the electronic structure of superionic conductors

我们已经将变分增广平面波（APW）方法的细节提供给公众。新方法通过最小化系统的总能量泛函（包括MT球的半径）来确定松饼-锡（MT）近似框架中的Kohn-Sham （KS）势。证实了该方法的基本思想适用于其他电子结构计算方案，如LMTO和ASW方法的KS势参数可调。然后将变APW方法应用于一系列贵金属卤化物，证明了d壳层的多极极化性和p-d杂化的弱点的结合是产生超离子电导率的主要原因。我们引入了一个新的参数，称为广义共价，它量化了宿主卤素原子的p态产生的p能带和贵金属原子的d态产生的d能带之间的杂化强度。广义共价系统地解释了化合物所显示的离子电导率趋势。我们还对贵金属化合物的广义共价进行了紧密结合（TB）计算。适当选择TB参数可得到与第一性原理计算基本相同的结果。目前，我们正在开发一种基于TB近似的分子动力学代码，使我们能够在电子水平上研究材料中的离子传输；基于消息传递接口的并行计算在我们的研究范围之内。如何从变分APW计算中提取TB参数是一个有待解决的问题。

We have made details of the variational Augmented Plane Wave (APW) method available to the public. The new method determines the Kohn-Sham (KS) potentials in the framework of the muffin-tin (MT) approximation through minimization of the total energy functional of a system, including the radii of the MT spheres. It was confirmed that the fundamental idea of the method was applicable to other electronic-structure calculation schemes such as the LMTO and ASW methods with adjustable parameters for the KS potentials. The variaional APW method was then applied to a series of noble-metal halides to demonstrate that combination of multipole polarizability of the d shell and weakness of the p-d hybridization plays a primary role in giving rise to the superionic conductivity. We introduced a new parameter, called generalized covalency, which quantifies the strength of hybridization between the p bands arising from the p states of host halogen atoms and the d bands from the d states of noble-metal atoms. The generalized covalency systematically explains the trend of ionic conductivity as shown by the compounds. We have also carried out the tight-binding (TB) calculations for the generalized covalency in the noble-metal compounds. Appropriate choice of the TB parameters leads to the essentially same results as those obtained by the first-principle calculations. Currently we are developing a molecular dynamics code based on the TB approximation that enables us to study the ionic transport in materials at the electronic level ; parallel computation based on the Message Passing Interface is within our scope. How to extract the TB parameters from the variational APW calculations is a remaining issue to be addressed.