First-Principles Calculation for the Half Metallic Properties of La_2NbMnO_6

La_2VMnO_6 is measured to be insulating and ferrimagnetic experimentally. In this study, by substituting V with Nb, La_2NbMnO_6 is investigated using the density functional theory. The calculated results indicate that La_2NbMnO_6 is also ferrimagnetic and exhibits the half metallic properties due to the strong electron correlation of Mn. The valence states of Nb and Mn are assigned to be +4 and +2 in La_2NbMnO_6, respectively, which are different from V^3+/Mn^3+ in La_2VMnO_6.