Dynamical Structure Factor and Vibrational Normal Modes of SiO 2 Glass
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DYNAMICAL STRUCTURE FACTOR AND VIHBRATIONAL NORMAL MODES OF SiO 2 GLASS WEI JIN, RAJIV K. KALIA,
and PRIYA VASHISHTA
Concurrent Computing Laboratory for Materials Simulations Department of Physics & Astronomy and Department of Computer Science Louisiana State University, Baton Rouge, Louisiana 70803-4001
Abstract We study the atomic vibrational dynamics in silica glass (a-SiO 2 ) using moleculardynamics (MD) simulations and classical lattice dynamics method. The SiO 2 glasses were generated by molecular-dynamics and steepest-descent quench (SDQ) using an effective interatomic potential consisting of two-body and three-body interactions. The frequency and eigenvectors of vibrational normal modes are obtained by diagonalization of the dynamical matrix. The partial and total vibrational density of states (DOS), bond-projected DOS, participation ratio (PR), and neutron-weighted dynamic structure factor are calculated. The results are compared with inelastic neutron scattering experiments on SiO 2 glass. lIntroduction For the past several decades, crystalline and glassy states of SiO 2 have been the subject of much research effort [1-17]. Structural properties of SiO 2 glass have been extensively studied, both experimentally [2-4] and theoretically [11-19]. It is widely believed [1, 2] that the short-range structural order in a-Si0 2 is corner-sharing Si(0 1 / 2) 4 tetrahedral units, similar to those in crystalline forms [1] of silica. The atomic vibrational properties of a-Si0 2 is a more complex problem [14]. The presence of disorder strongly affects the atomic motion in glass. Various numerical [11-14, 16, 17] and analytical [15] methods, and a variety of experimental techniques (Raman [5] and Brillouin [6] scattering, infrared absorption and reflectivity [7] and inelastic neutron scattering [7-101) have been used to study atomic vibrations in Si0 2 glass. In this paper, we discuss results of out recent [20] simulation studies for the vibrational properties of SiO 2 glass. Our primary interest in this work is the computation of neutronweighted dynamical structure factor, S.(q, wo)as a function of w and q, and the vibrational density of states. The dynamic structure factor can be compared directly with results from inelastic neutron scattering experiments.
Molecular-Dynamics Simulations In the present study we have used the molecular-dynamics method [21] in conjunction with the recently developed [18] effective interatomic potential for Si0 2 . The potential consists of two- and three-body terms V((ri}):) T i
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