Understanding and predicting the properties of transition metal oxides is one of the most challenging activities of chemical and materials science. These systems in bulk and nanostructured form possess a wide range of complex, but often desirable, structural, electronic, and optical properties, which usually result from the subtle interplay between their orbital, spin, charge, and lattice degrees of freedom. They have been the focus of many theoretical and experimental studies based on their use in such diverse applications as high temperature superconductors, catalysts, dielectrics, and multi-ferroic materials. More recently, transition metal oxides have emerged as a promising class of materials for a variety of photonic and opto-electronic applications such as solar cells, light-emitting diodes, transparent conductors, photovoltaics and photocatalysts. Such applications, which require prediction and characterization of various excitations resulting from light-matter interactions, call for the development and refinement of accurate computational methods to help in the interpretation of experimental data as well as the design and discovery of new molecular systems and materials with useful functionalities.
Motivated by the growing need for accurate modeling of excited states of transition metal oxide nanostructures, the overall goal of this research program is to investigate the impact of various computational and theoretical techniques employed within a many-body perturbation theory approach, called the GW-BSE formalism. This formalism, which has provided rather accurate predictions and insights for light-matter interactions in relatively simple systems composed of s and p valence electrons, is theoretically less understood and computationally very demanding for describing such interactions in transition metal oxide systems due to the presence of d valence electrons which experience strong electron correlations. Therefore, this research program will fill an important knowledge gap, as it will advance our understanding of many-body perturbation theory as applied to a set of technologically important molecular systems in which d−electron correlations play a significant role in giving rise to their unique electronic and optical properties.
The particular systems which will be studied using GW-BSE formalism include monoxide and dioxide clusters of transition metal elements from the 3d series (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn), negatively charged clusters of copper, vanadium, and chromium oxide clusters containing up to ~25 atoms, as well as bulk-truncated Cu2O and Ag2O nanocrystals, which have received recent attention due to their potentially useful photovoltaic and photocatalytic properties. Comparing the predictions from several variants of the GW-BSE formalism with each other, available high-resolution photoelectron spectroscopy data, and high-level quantum chemistry computations will help us identify the level of theory and approximations that are needed to achieve an ideal balance between accuracy and computational demand, and thus pave the way for unbiased and reliable predictions of excited state properties in these technologically important molecular systems.
