The electronic structure and magnetism of eskolaite are studied by using first-principles calculations where the on-site Coulomb interaction and the exchange interaction are taken into account and the LSDA＋U method is used. The calculated energies of magnetic configurations are very well fitted by the Heisenberg Hamiltonian with interactions in five neighbour shells; interaction with two nearest neighbours is found to be dominant. The Neel temperature is calculated in the spin-3/2 pair-cluster approximation. It is found that the measurements are in good agreement with the calculations of lattice parameters, density of states, band gap, local magnetic moment, and the Neel temperature for the values of U and J that are close to those obtained within the constrained occupation method. The band gap is of the Mott-Hubbard type.
This paper studies the structure and electronic properties of Li4Ti5O12, as anode material for lithium ion batteries, from first principles calculations. The results suggest that there are two kinds of unit cell of Li4Ti5O12： n-type and p-type. The two unit cells have different structures and electronic properties： the n-type with two 16d site Li ions is metallic by electron, while the p-type with three 16d Li ions is metallic by hole. However, the Li4Ti5O12 is an insulator. It is very interesting that one n-type cell and two p-type cells constitute one Li4Ti5O12 supercell which is insulating. The results show that the intercalation potential obtained with a p-type unit cell with one additional electron is quite close to the experimental value of 1.5 V.
Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ are investigated using density- functional theory calculations. Results indicate that nonstoichiometric LiNi0.5Mn1.5O4-δ and stoichiometric LiNi0.5Mn1.5O4 exhibit two different structures, i.e., the face-centred cubic （Fd-3m） and primitive, or simple, cubic （P4332） space groups, respectively. It is found that the magnetic ground state of LiNi0.5Mn1.5O4（P4332 and Fd-3m） is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the [110] direction whereas they are antiferromagnetic with respect to each other. We demonstrate that it is the presence of an O-vacancy in LiNi0.5Mn1.5O4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi0.5Mn1.5O4 with the P4332 space group.
