Electronic Structure of LiMnO$_{2}$: A Comparative Study of the LSDA and LSDA+U methods

A first-principles electronic structure study of orthorhombic, monoclinic and rhombohedral LiMnO$_{2}$ has been carried out using the full-potential linearized augmented plane-wave method. The exchange and correlations have been treated within the local spin-density approximation (LSDA) and the LSDA+U methods. In the LSDA, the stable ground state is antiferromagnetic insulator for the orthorhombic and monoclinic structures but is ferromagnetic metal for the rhombohedral structure. The LSDA+U, on the other hand, predicts the ground state to be an antiferromagnetic insulator for all structures. We find that strong correlations change the density of states dramatically around the Fermi level. The LSDA+U predicts the nature of band gap to be a mixture of charge transfer and Mn $d \leftrightarrow d$ like excitations for orthorhombic and monoclinic LiMnO$_{2}$ and Mott-insulator for rhombohedral LiMnO$_{2}$ in agreement with the available experimental results. The inclusion of U increases the magnetic moment on Mn and gives a value in better agreement with experiment. However, Mn valency is not affected by the inclusion of U. We have also calculated X-ray emission photoelectron spectra for the orthorhombic and monoclinic LiMnO$_{2}$ by the LSDA and the LSDA+U methods. We find that LSDA+U gives better agreement with the available experimental results.