%0 Journal Article
%T A Theoretical Study of Bulk Tungsten (W) Based on Momentum Transfer ( -Dependent)
%A D. P. Rai
%A R. K. Thapa
%J Advances in Optics
%D 2014
%R 10.1155/2014/814909
%X The ground state electronic properties of bulk (W) were studied within the density functional theory (DFT). We have also analyzed the momentum- (q-) dependent loss function, dielectric constant, and optical conductivity (OC) within TD-DFT random-phase approximation (RPA). The loss function is plotted in the energy range 0¨C55£¿eV. The energy loss function spectrum shows four prominent peaks, two lower peaks below along with two sharp peaks above 30£¿eV. The different nature of peaks depends on the momentum transfer q. The peak caused by interband transition showed a less pronounced dispersion. From the dielectric function curve we have predicted the plasmon excitation at around 1.75£¿eV and calculated the corresponding plasma frequency £¿s£¿1. 1. Introduction Tungsten (derived from the Swedish phrase ¡°tung sten,¡± meaning heavy stone) is a hard, brittle, steel-grey metal that is difficult to work with in the very pure state, unless it is malleable and ductile [1]. Tungsten is an interesting element whose unique physical properties make it an essential component in many industrial applications. Critical properties include very high melting point, very high density, hardness close to diamond, thermally stable, and excellent conductor [2]. The electronic structure and Fermi surface of tungsten have been studied extensively, experimentally and theoretically [3¨C7]. Some of the metallic crystals exhibit optical properties due to the interplay between electronic plasma screening and geometrical scattering effects [8]. Under suitable circumstances, this might be used to enhance thermal emission of photons in the visible region relative to lower frequencies and serve as a lighting technology [9]. Optical measurements provide several important microcharacteristics of the conduction electrons, their plasma frequency, and the relaxation frequency, as well as the energy gaps between the bands in the region of allowed electronic transitions. The optical properties of bulk polycrystalline tungsten have been investigated by Roberts [10] in the 0.5¨C0.8£¿¦Ì region and also by Lenham and Treherne [11] in the 0.35¨C20£¿¦Ì region. Juenker et al. measured the reflectivity of tungsten from 0.577 to 0.05£¿¦Ì [12]. Sudarshan et al. studied the angular distribution of backward reemitted positrons from a W(100) single crystal which showed that the mean energy of the emitted positrons increased with angular deviation from normal, with incident positron energies of 250 and 600£¿eV. The increase in the energy is explained in terms of energy-dependent refraction of positrons traversing the
%U http://www.hindawi.com/journals/ao/2014/814909/