First Principles Study of Electronic Structure and Magnetic Properties of TMH (TM = Cr, Mn, Fe, Co)

First principles calculations are performed using a tight-binding linear muffin-tin orbital (TB-LMTO) method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of transition metal hydrides (TMH) (TM = Cr, Mn, Fe, Co). The structural property, electronic structure, and magnetic properties are investigated. A pressure induced structural phase transition from cubic to hexagonal phase is predicted at the pressures of 50？GPa for CrH and 23？GPa for CoH. Also, magnetic phase transition is observed in FeH and CoH at the pressures of 10？GPa and 180？GPa, respectively. 1. Introduction Metal hydrides have been attracting attention of scientists for decades. Their physical properties are interesting from both fundamental and practical points of view. Many transition metals react readily with hydrogen to form stable metal hydrides [1]. Metal hydrides are of intense scientific and technological interest in the view of their potential application, for example, for hydrogen storage, in fuel cells and internal combustion engines, as electrodes for rechargeable batteries, and in energy conversion devices. Hydrides for hydrogen storage need to be able to form hydrides with a high hydrogen to metal mass ratio but should not be too stable, so that the hydrogen can easily be released without excessive heating [2]. Among those, the metal hydrides are of particular interest due to their application in hydrogen storage for fuel cells [3, 4]. The physical properties of metal hydrides are quite interesting from the practical point of view. For example, the density of hydrogen in metal hydrides is larger than that in liquid hydrogen [5]. Previously the first principles calculations were performed for metal dihydrides with the fluorite structure [6, 7]. The stability and electronic structure of the transition-metal hydrides were reported [8]. Phase transformations, crystal and magnetic structures of high-pressure hydrides of d-metals were analyzed by Antonov [9]. -CrH and -CrH hydrides were prepared electrolytically and studied by neutron diffraction and inelastic neutron scattering at liquid helium temperatures [10]. Previously we have investigated the pressure induced magnetic phase transition in hexagonal FeH and CoH [11]. In this work, the structural, electronic, and magnetic properties of 3d transition metal hydrides (CrH, MnH, FeH, CoH) are investigated using TB-LMTO method. The weight percentage of hydrogen in Cr, Mn, Fe, and Co is also calculated. 2. Computational Details The TB-LMTO (tight-binding linear