First-principles Studies Of Low-Dimensional Alkaline Earth Metal Nitride Electrides

Advance quantum computational methods such as density functional theory provide a rapid way for materials design simulations.In this dissertation,we employed density functional theory calculations for investigating electronic and chemical properties of an exotic class of ionic compounds called electrides.Electrides are the unique class of ionic compounds with excess electrons as anions,without a nuclear core.Such materials in recent have seen a rapid development particularly aided by density functional theory simulations.More focused on their low dimensional atomistic models we unearthed some interesting ab intio information,which we expect to deliver proof to concepts and will back up experimentalists describing doable pathways for novel electride materials based designs.In the first chapter,a complete review of electride material development in the past is made.Starts from works done by Dye et al.for production of a first of its kind organic class of electrides materials.Latter Hosono et al.coming up with breakthrough of air and room temperature stable inorganic electride.Electeides are striking electroactive materials shown to hold potential for implementation in numerous applications;we also tried to cover such available literature in this chapter.The last section of this chapter covers a fresh look at opening up of dimensionality in inorganic eletrides with the discovery of Ca2N layered electride.Since that many density functional theory assisted high throughput database screenings and totally density functional theory simulations designed novel electride materials from macro to nanoscale regime have been produced.One big challenge faced by such layered electrides is their ambient environment sensitivity.In the 2nd chapter,a theoretical background of density functional theory is introduced.Especially to describe with exchange-correlation functionals in the esteems of the level of accuracy required for the approximations to describe weak interactions,is presented.In addition,we introduce software packages used to implement first-principles calculations in our study.We also summarize details of corresponding technical details and post-processing software employed in our work.The end of this chapter,focus on theoretical descriptor normally encountered particularly for design and description electrides.In chapter 3,we focused on Ca2N nanotubes theoretical design of achieving one-dimensional electron gas in free space.We systematically proposed nomenclature of zigzag or armchair configuration for Ca2N nanotubes.From a stability point of view,we calculated curvature induced strain energies and atomic binding energies per atom as a function of nanotube diameters.We also compare strain energy to MoS2 and WS2 nanotubes,which show it to be lower for Ca2N nanotubes.Curvature induces electronic band folding in Ca2N nanotubes forming intrinsically occupied superatom states across nanotube cross sections.Such states could be closely related to nearly free electron superatom like states in hollow molecular structures such as C60 and CNTs.In contrast to superatom states of CNT,Ca2N nanotube superatom states are intrinsically occupied well below Fermi level.But one big drawback is such a chemical system face high chemical instability to the ambient environmental conditions which requires a proper preservation scheme.In chapter 4,we focused on the chemical preservation of our newly designed Ca2N nanotubes from chapter 3.We made a composite of(6,6)Ca2N nanotube embedded inside(17,17)CNT system.We performed geometrical optimizations and results show no type of significant deformations.Through systematic calculations of electronic band structure,electronic band decomposed charge densities and electron localization function we confirm preservation of one-dimensional electron gas inside Ca2N@CNT composite system.Further,we also confirmed the superatom states are also well preserved inside this theoretically designed composite system.We also test ambient environment gases such as O2,H2O and N2 adsorption on the Ca2N@CNT system.Overall we showed that Ca2N@CNT protected composite system with flexible occupation statuses are expected to have a great potential in various application fields including catalysis and electronics.In chapter 5,we explore tri alkaline earth metal nitride newly revealed electride.Structurally their crystal lattice is formed by[M3N]+3 ID cationic nanorods held together by delocalized excess anionic electrons at large crystal voids.We report a first-principle based study of M3X compounds and predict dynamically stable 3 members to a very new family of quasi one-dimensional electride nanorods.Stability of 1D nanorods is strictly related to metal to non-metal atom electronegativity difference.Through careful electronic structure analysis,we also explain how these superatom nanorods form basic building blocks of the bulk phase.Our study show only three out of four stable structures are electride whereas in Ba3P nanorods prefer to bind through metallic bonds.Through a fundamental understanding of electride role in ammonia synthesis,we also test M3X character for hydride ion store ability.Ba3H3N is the only system found dynamically stable in our study.Ba3N ability to take up hydrogen as hydrides itself offers the potential for low-temperature catalytic applications.