Quantum-Chemical Investigation of the Metal-Insulator Transition in realistic Low-Dimensional Systems

这个联合项目旨在通过对石墨烯纳米岛和一维原子链等系统的理论研究，提高我们对低维系统中金属-绝缘体转变（MIT）的理解。该主题处于微电子学和分子电子学的边缘，其中所研究系统的化学成分的细节可以对MIT的存在（或不存在）及其对外部扰动的敏感性产生巨大影响。我们的目标是分析和理解技术相关性系统中的行为变化。我们还打算为石墨烯和金属组合形成的新材料的设计提供支持。为了有一个现实的描述系统，我们解决了全电子薛定谔方程与量子化学方法，从全组态相互作用（FCI）通过各种近似多参考方法，半经验方法非常大的系统（专业知识的Evangelisti组）。为了使系统地改进的基于波函数的相关方法在大型甚至周期性系统中的应用变得可行，我们将采用增量法。这种特殊形式的局部相关方法扩展了系统的相关能量，从单个中心（单中心项），从一对中心（双中心项）等的增量，并且可以合理地快速收敛，甚至对于大块金属（保卢斯小组的专业知识）。MIT可以用不同的指标来表征，如能隙、电极化率、位置算符的涨落（局域化）和粒子-空穴熵。所有这些指标都可以并将以从头开始的方式计算，并对不同系统和不同类型的多边贸易协定进行比较。

This joint project aims to improve our understanding of the metal-insulator transition (MIT) in low-dimensional systems through theoretical investigations for systems like graphene nanoislands and one-dimensional atomic chains. The topic is at the borderline of microelectronics and molecular electronics, where details of chemical composition of a system under study can have a huge influence on the existence (or absence) of a MIT, and on its sensitivity to external perturbations. Our aim is to analyze and understand the change in the conducting behavior in systems of technological relevance. We further intend to provide support for the design of new materials formed by a combination of graphene and metals. In order to have a realistic description of the system, we solve the full electronic Schrödinger equation with quantum-chemical methods, ranging from full configuration interaction (FCI) via various approximate multi-reference methods to semiempirical methods for very large systems (expertise of the Evangelisti group). To make feasible the application of systematically improvable wavefunction-based correlation methods for large or even periodic systems, we will apply the method of increments. This special version of a local correlation method expands the correlation energy of the system in terms of increments from a single center (one-center term), from a pair of centers (two-center term), and so on, and can be made to converge reasonably quickly even for bulk metals (expertise of the Paulus group). The MIT can be characterized by different indicators, such as energy gap, electric polarizability, fluctuation of the position operator (localizability), and the particle-hole entropy. All these indicators can be, and will be, calculated in an ab initio manner and compared for different systems and different types of MITs.