releasing the outermost Z1 electrons per atom to form the valence band. As a result, conduction electrons carrying negative charges are uniformly distributed over any atomic site with equal probability densities and maintain charge neutrality with the array of ions with positive charges. When an impurity atom of valence Z2 is introduced, the periodic potential is disturbed, conduction electrons are scattered and a screening potential is formed where U(r) is the potential of the electrons in distance r, 1/λ is the screening radius and . The Fermi surface of the pure metal is constructed under the assumption that the wave vector k of the Bloch electron is a good quantum number. But alloying destroys the periodicity of the lattice potential and thus results in scattering of the Bloch electron. The wave vector k changes upon scattering of the Bloch electron and can no longer be taken as a good quantum number. In spite of such fundamental difficulties, experimental and theoretical works have provided ample evidence that the concept of the Fermi surface and Brillouin zone is still valid even in concentrated crystalline alloys In an alloy of atoms A and B, an intermetallic compound super-lattice structure tends to be formed. The chemical bonding between the unlike atoms leads to a very strong potential of the form where is the potential on position due to ion X, whose position is specified by . X here stands for either A or B, so that indicates the potential of ion A. The RBM assumes , hence ignores the difference in the potential of ions A and B. Thus, the electronic structure of the pure metal A is assumed to be the same as that of the pure metal B or any compositions in the alloy A–B. The Fermi level is then chosen so as to be consistent with the electron concentration of the alloy. It is convenient to divide the predictions of the rigid-band model into two categories, geometric and density of states. The geometric predictions are those that use only the geometric properties of the constant energy surfaces. The density-of-states predictions are related to those properties which depend on the density of states at the Fermi energy such as the electronic specific heat. Geometric structure In a pure metal the eigenstates are the Bloch functions Ψk with energies ek. When the periodicity of the pure metal is destroyed by alloying, these Bloch