Progress in ab initio calculations of polarons: reduced dimensionality and many-body effects

Polarons are among the most well-known quasiparticles in solid state physics, and play an important role in the electronic, optical, and transport properties of many classes of materials, from organics to oxides. Recently we introduced an ab initio formalism to investigate small and large polarons on the same footing [1,2]. This formalism does not suffer from the delocalization error introduced by self-interaction in density functional theory, and employs density-functional perturbation theory to circumvent the need for large supercell calculations. In this talk I will describe further progress on our ab initio theory of polarons on two fronts. Firstly, I will discuss the role of dimensionality on the electron-phonon coupling and the energetics and size of polarons [3]. For this discussion I will illustrate recent methodological developments on the calculations of polar electron-phonon interactions in two dimensions. Secondly, I will discuss our efforts to establish a many-body Green’s function framework for the ab initio polarons equations of Refs. [1,2]. I will show how polaron formation, phonon-induced band gap renormalization, and phonon satellites in photoelectron spectroscopy can be rationalized within a unified conceptual framework. I will also discuss how the modern ab initio theory of polarons relates to earlier model-Hamiltonian approaches to the polaron problem [4].