CAREER: State-of-the-art Quantum Calculations on a Novel Class of Super-atoms: Discovering Exotic Chemical Bonding Schemes and Proposing New Two and Three Dimensional Materials

Auburn University, Auburn AL

Investigators

Abstract

New materials are in high demand in modern industry. There is a particular need for new approaches to building batteries and other electronics. One type of new material may be formed through the interaction of metal atoms dissolved in liquid ammonia. In a normal atom, negatively charged electrons orbit around a positively charged central nucleus. In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Evangelos Miliordos of Auburn University is studying concentrated metal-ammonia solutions, where an electron from the metal atom moves so far from the nucleus that it orbits the outermost edge of a nearby ammonia molecule. The metal atom and ammonia molecule form a large combined structure, where the atoms of the molecule act like the nucleus of a single super-sized atom. Professor Miliordos is applying the principles of quantum mechanics to study the physical and chemical properties of individual metal-ammonia molecules. The knowledge from these theoretical studies can be used to guide experiments on this unique class of chemicals, which are known as solvated electron precursors (SEP). Future applications are possible in the chemistry of batteries/solar cells, catalysis, and quantum computing. Students engaged in the project learn modern computational chemistry methods and become experts in transition metal chemistry. Professor Miliordos is also developing modules based on the research results that will introduce these groundbreaking concepts to high school students. The project focuses on the performance of high-level electronic structure calculations (density functional theory, multi-reference configuration interaction, perturbation theory, and coupled cluster approaches) of the properties of transition metals coordinated with a number of ammonia, amine, polyamine, or other ligands. As the ligands approach the metal center, they displace some of the metallic valence electrons to the periphery of the complex making bound Rydberg molecular systems. The diffuse electrons occupy hydrogenic-type orbitals centered around the metal-ammonia core. In the lowest energy states s-, p-, d-, f-, and g-shaped orbitals are identified within a shell model resembling that of the Jellium or nuclear-shell models: 1s, 1p, 1d, 2s, 2p, 1f, 2d, 3s, and 1g. The electronic configuration for the ground and several low-lying electronic states is investigated and accurate excitation energies are calculated to explain existing and assist future experimental studies. The stability of these transition metal complexes is examined in terms of metal-ligand binding energies and activation energies towards the release of molecular hydrogen. The broader impacts of this work include potential societal benefits from an increased understanding of transition metal chemistry, as well as opportunities for the training of students in the use and critical selection of the existing electronic structure techniques. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.