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Density functional theory study of phase stability, vibrational and electronic properties of $Mo_3Al_2C$

Based on density functional theory the noncentrosymmetric superconductor Mo_3Al_2C in its well established β-Mn type ($P4_{1}32$) crystal structure is investigated. In particular, its thermodynamical and dynamical stabilities are studied by calculating lattice vibrations within the harmonic approximation. It is found that the fully stoichiometric compound is dynamically unstable. However, compounds with carbon vacancies, i.e., Mo_3Al_2C_{1-x}, can be dynamically stabilized for vacancy concentrations x > 0.09. By means of a simple thermodynamical model we estimate x ~ 0.13-0.14 for Mo_3Al_2C_{1-x} at the experimental preparation temperatures. The influence of the carbon vacancy concentration on the electronic structure is investigated.