Date of Award

August 2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Dennis W. Bennett

Committee Members

Peter Geissinger, Mark Dietz, Arsenio A. Pacheco, Jorg Woehl

Abstract

The desire to rationalize and explain the complex structures that form in solid states has motivated many to explore collections of structures with similar topologies but with differing compositions in order to determine whether or not similar chemical bonding was responsible for the structures. The Zintl-Klemm Concept, the Extended Zintl-Klemm Concept Model-1, and the Extended Zintl-Klemm Concept Model-2 attempt to rationalize and predict the structure of a group of intermetallics, referred to as Zintl Compounds, and their oxides based on simple electron counting schemes and with the introduction of pseudo-atoms.

This study looks at the electronic structure of a set of Zintl Compounds and their oxides in order to determine if the internal electronic structure of these solids mirror the predictive models used to rationalize their structure and the behavior exhibited in terms of the pseudo-atom approach used to arrive at the physical structure of the solid.

The electronic structure was attained by analyzing the charge density from three ab initio DFT programs via the Laplacian, the Bader Charges (by applying Bader's Atoms in Molecules Analysis), and difference charge densities.

The three programs utilized in this study were: FLAIR, CRYSTAL14, and VASP. Both FLAIR and CRYSTAL14 are all-electron programs that take advantage of a crystal's symmetry to arrive at convergence. While FLAIR is a Full-potential Linearized Augmented Plane Wave (FLAPW) program, CRYSTAL14 is a molecular orbital computational program, using atomic basis sets to model the atoms in the crystal and calculate the wave functions. VASP, while also using plane wave basis sets, approximates the core electron density with pseudo-potentials –therefore using only the valence electrons when calculating the electron density. These three programs were used to verify if computational bias was present within the results attained in the analysis of these solids.

The comparison between programs demonstrated that even though different computational methods were used, the information was largely equivalent, imparting the same information for the solids compared. The theoretical analysis on the concepts determined that the Zintl-Klemm Concept and the Extended Zintl-Klemm Concept Model-1 were able to adequately rationalize the bonding and pseudo-atom behavior proposed, but that when examining the oxides the bonding posited by the Extended Zintl-Klemm Concept Model-2 was not seen. In other words, the electronic structure in the solids analyzed with the Zintl-Klemm Concept and the Extended Zintl-Klemm Concept Model-1 mirrored the rationalizations used to explain the physical structure of these solids and their behavior.

While assessing these solids, unexpected and unusual behavior was observed with solids containing calcium. The calcium atoms within the structures seemed to acquire charge, becoming anionic. This behavior was seen even in the presence of oxygen.

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