الفهرس 
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Abstract
We present in this thesis a first-principles study on the magnetic properties, the electronic structure and the elastic properties (e.g. bulk modulus) at ambient and higher hydrostatic pressures of 3d metal- based compounds using the well known Full-Potential Local-Orbital minimum basis (FPLO) code. The systems under study are the ferromagnetic element Fe, paramagnetic element Y and the Y-Fe based compounds: YFe2 and the hypothetical YFe5. The LSDA and GGA approximations, as implemented in FPLO-09 are used throughout the scalar relativistic calculation in this work. For each of these elements and compounds self-consistent calculations are performed to study some or all of the following where appropriate: energy dependence on the c/a ratio at constant volume to obtain the minimum energy, energy dependence on unit cell volume or primitive volume, dependence of magnetic moment on unit cell volume or primitive volume , dependence of the exchange –correlation energy on both the cell volume and its magnetic moment, density of states(DOS) and electronic energy band structure, dependence of magnetic moment on hydrostatic pressure, and charge and spin density maps using Wien2k for the equilibrium lattice constants. In addition we have calculated other physical quantities of interest e.g. the electronic heat capacity coefficient, the bulk modulus and its first pressure- derivative. For the ferromagnetic element Fe we studied the properties of bcc, fcc and hcp phases in order to investigate the possibility of occurrence of magnetism in different crystal structures of the same element. Our study shows that the magnetic phase of Fe element and Y-Fe compounds is more stable than the nonmagnetic phase, and that the application of pressure has a prominent effect on its magnetic and electronic properties, e.g. the reduction of the magnetic moment and finally the disappearance of the ferromagnetism. Our results have been compared with the results of experiments, which are available for nonhypothetical compound on these systems and other ab initio calculations using other known electronic structure packages. These comparisons show a good deal of agreement between the present work and other published investigations. This thesis is composed of three chapters, an abstract and a conclusions section. The first one deals with a necessary introduction to the subject, the theoretical background and calculation method are outlined in chapter 2. We present our results in chapter 3 and discuss them in the light of available other first – principles calculations and experimental data.