First principles study of electronic structure, structural and optical properties of Mg_3Si_2O_5(OH)_4

摘要

We present first principles calculations of structural properties, electronic structure, and optical properties of hexagonal Mg_3Si_2O_5(OH)_4 by using the Vienna ab initio simulation package (VASP) within the generalized-gradient approximation (GGA). Using experimentally established lattice parameters as input, full optimization of the geometry of the lattice has been performed. A difference of 3.6% between calculated and experimentally measured volume of the unit cell was found in the present calculations. The total density of states was calculated using the optimized lattice parameters. From that Mg_3Si_2O_5(OH)_4 was found to be a wide-band gap material with the calculated band gap exceeding 4 eV. The orbital and site projected density of states show the topmost valence band contains sharp peaks belonging to O atoms, which reveals the ionic nature of the chemical bonds in Lizardite. The lowest conduction band has a strong contribution from the Si 4 s hybridized with O 2 s electrons. In addition, reflectivity, absorption coefficient, electron-electron loss function, the extinction coefficient, and the refractive index are also studied. We show that the optical properties of Lizardite are isotropic and do not depend on direction. The absorption and reflectivity values are almost zero in the photon energy range 0-4 eV, whereas the Refractive index is ～1.58. So, if combined with Si, Mg_3Si_2H_4O_9 will possess good antireflection properties while the present of hydrogen will be important to passivate dangling bonds which are at the surface and other bulk defects in Si.