Electronic Band Structure, Antiferromagnetism, and the Nature of Chemical Bonding in La2CuO4

The electronic band structure of orthorhombic compound La2CuO4, which is the parent for a number of high-temperature superconductor families, has been calculated in terms of the density functional theory using the WIEN2k program package. Calculations have been performed by means of two exchange-correlation functionals. The former is a sum of the Tran- and Blaha-modified Becke-Johnson exchange potential and correlations in a local approximation, whereas the latter is the Perdew-Burke-Ernzerhof functional. Calculations taking into account spin polarization have shown the presence of an antiferromagnetic ground state in orthorhombic La2CuO4. Using the former functional, the magnetic moment of copper atoms and a semiconductor gap have been found to be M-Cu = 0.725 & mu;(B) and E-g = 2 eV. The latter has yielded M-Cu = 0.278 & mu;(B) and E-g = 0. Calculations results for the optical properties of orthorhombic La2CuO4: the electron energy losses, the real part of optical conductivity, and reflection coefficient, are in good agreement with experimental data. The calculated spatial distribution of the charge density in orthorhombic compound La2CuO4 has been analyzed with the aim of finding critical saddle points with parameters making it possible to classify the types of chemical bonds in crystals. The set of critical point parameters for orthorhombic La2CuO4 has turned out to be similar to that previously found by us for tetragonal La2CuO4 and related high temperature superconductors. In particular, the positive sign of the charge density Laplacian at bond critical points indicates the absence of covalent bonding in La2CuO4 according to the chemical bond classification proposed by Bader in his "Quantum Theory of Atoms in Molecules and Crystals."