Electrical Conductivity and Carrier Mobility for Strongly Anharmonic Materials from First Principles

Strong anharmonicity typically reflects that the atoms don't just vibrate around a single minimum of the potential-energy surface, but that they also visit other minima.[1] The latter may be called local precursors of other crystal phases, or "phase-transition embryos". Then, phonons are not a good concept and phonon-based perturbation theories will fail. As many materials exhibit the described anharmonic behavior, we implemented the Kubo-Greenwood (KG) approach into the highly efficient all-electron code FHI-aims [2]. The underlying ab initio molecular dynamics and statistical mechanics take into account all orders of anharmonicities and electron-vibrational couplings.

In particular, we discuss in this talk the definition of carrier mobility in the KG framework and the developed numerical strategies employed to overcome the notoriously slow convergence of the phase-space and Brillouin-zone integrals in crystalline solids. Using SrTiO3 and other strongly anharmonic materials, we demonstrate the capabilities and predictive power of the KG approach and investigate the influence of the chosen exchange-correlation functional on the obtained conductivities and mobilities. Eventually, we analyze the observed trends and explain the effects in terms of self-energy shifts and broadenings.[3]