Electronic Principles of Some Trends in Properties of Metallic Hydrides

Due to their extensive present, important and versatile potential applications, metal hydrides (MH)are among the most investigated solid-state systems. Theoretical, numerical and experimental studieshave provided a considerable knowledge about their structure and properties, but in spite of that, thebasic electronic principles of various interactions present in MH have not yet been completelyresolved. Even in the simplest MH, i.e. alkali hydrides (Alk-H), some trends in physical properties,and especially their deviations, are not well understood. Similar doubts exist for the alkaline-earthhydride (AlkE-H) series, and are even more pronounced for complex systems, like transition metaldopedAlkE-H, alanates and borohydrides. This work is an attempt of explaining some trends in thephysical properties of Alk-H and AlkE-H, employing the Bader analysis of the charge distributiontopology evaluated by first-principle all-electron calculations. These results are related to somevariables commonly used in the explanation of experimental and calculated results, and are alsoaccompanied by simple tight-binding estimations. Such an approach provides a valuable insight inthe characteristics of M-H and H-H interactions in these hydrides, and their possible changes alongwith external parameters, like temperature, pressure, defect or impurity introduction. The knowledgeof these basic interactions and processes taking place in simple MH are essential for the design andoptimisation of complex MH-systems interesting for practical hydrogen storage applications.