In this research, first-principle calculations have been performed to study the geometry structure and electronic properties of ZnO. All possible exchange-correlation energy functionals were used to perform geometry optimization of ZnO in order to find the efficient calculation conditions. Bandgap energy, density of states (DOS), projected DOS (PDOS)
and other properties of ZnO were also calculated and discussed. The calculated band-gap value of ZnO is less than 1.0 eV, much smaller than experimental value of 3.37 eV
while the PDOS results indicate the important roles of O 2p and Zn 3d orbitals in ZnO band structures. The well-known limitation of band-gap value calculations using Density Functional Theory (DFT) was solved by applying Hubbard potential on Zn 3d and O 2p orbitals. A full investigation with Hubbard value varying from 0.5 to 10 eV has been performed and the selected value is 8.0 eV for both Zn 3d and O 2p electrons.