Ab Initio Vibrational Dynamics of Strongly Anharmonic Materials

The atoms that compose molecules and crystalline materials are always vibrating. The quantum mechanical manifestations of these vibrations are called phonons. The properties of phonons, especially how they interact with one another or with electrons in the material, determine a number of technologically important properties, including those of solar cell materials that efficiently absorb light, thermoelectric materials that can turn waste heat into usable electricity, or superconducting materials that can transport electricity without resistance. Unfortunately, predicting these promising behaviors by computer simulation is very difficult when these vibrational interactions are strong. This work will develop a new computational method that will be able to simulate the vibrational properties of crystalline materials accurately and efficiently, called vibrational dynamical mean-field theory. This method is the analog of an existing state-of-the-art method for the quantum mechanical description of strongly interacting electrons, indicating a promising future in the simulation of strongly interacting phonons. This computational method will be implemented in an efficient, open-source software package and, upon completion, will be used to study halide perovskites for solar energy, thermoelectric materials for the recovery of waste heat, and hydrogen-containing materials for high-Tc superconductivity.