H. Hamedian - Department of Physics, Islamic Azad University, Science and Research Branch Khuzestan, Ahvaz
H. Salehi - Department of Physics, Shahid Chamran University, Ahvaz

AMnO3 compounds, like LaMnO3 and CaMnO3, have a crystal structure that is of the perovskite type, see Figure 1. LaMnO3 is the mother material of the colossal magnetoresistance manganites [1]. LaMnO3 has three current orthorhombic, cubic and tetragonal structures and all of them have approximately the same chemical properties, but their crystalline properties are different. LaMnO3 has different structures in low and high temperatures shown in the Figure1. The LaMnO3 structure is orthorhombic in low temperature (Figure 2a) with the experimental values of the lattice parameters c = 7.668Å, b = 5.742Å and a = 5.532Å [2] and there are some effective specifications for it such as John – Teller Sinuosity [3] plus the sinuosity and turning against the MnO6 octahedra and if these effects are ignored , the orthorhombic structure converts to a tetragonal (Figure 2b) with lattice constants a = b = 5.582Å, c = 7.894Å. In high temperature (Above 750K) LaMnO3 converts to ideal perovskite structure (pm 3 m) with atom 5 in each primary cubic cell (Figure 2c) with experimental lattice constant a0 = 3.95Å [2]. In this paper, electronic structure LaMnO3 in the tetragonal phase was investigation. Calculation by using the perturbation density functional theory and Quantum Espresso package. The calculations include the density of state and electron cloud density.