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Electronic Structures, Born Effective Charges and Spontaneous Polarization in Magnetoelectric Gallium Ferrite

We present a theoretical study of the structure-property correlation in gallium ferrite, based on the first principles calculations followed by a subsequent comparison with the experiments. Local spin density approximation (LSDA+U) of the density functional theory has been used to calculate the ground state structure, electronic band structure, density of states and Born effective charges. Calculations reveal that the ground state structure is orthorhombic Pc21n having A-type antiferromagnetic spin configuration, with lattice parameters matching well with those obtained experimentally. Plots of partial density of states of constituent ions exhibit noticeable hybridization of Fe 3d, Ga 4s, Ga 4p and O 2p states. However, the calculated charge density and electron localization function show largely ionic character of the Ga/Fe-O bonds which is also supported by lack of any significant anomaly in the calculated Born effective charges with respect to the corresponding nominal ionic charges. The calculations show a spontaneous polarization of ~ 59 microC/cm^2 along b-axis which is largely due to asymmetrically placed Ga1, Fe1, O1, O2 and O6 ions.