TY - JOUR

T1 - Dynamic structure factor of vitreous silica from first principles

T2 - Comparison to neutron-inelastic-scattering experiments

AU - Pasquarello, Alfredo

AU - Sarnthein, Johannes

AU - Car, Roberto

PY - 1998

Y1 - 1998

N2 - Using a first-principles approach, we study the vibrational properties of vitreous (Formula presented) which are measured in neutron-scattering experiments. We adopt a model structure consisting of corner-sharing tetrahedra, which was previously generated using first-principles molecular dynamics. We calculate the dynamic structure function (Formula presented) as a function of wave vector (Formula presented) and energy (Formula presented) by taking explicitly into account the correlations between different atoms as given by the normal modes. The effects of temperature and finite displacements are also considered. Overall, the agreement with experiment is very good, as illustrated by the comparison for the density of states. However, the calculated and measured (Formula presented) differ in some cases up to a factor of 2 in absolute intensity. Nevertheless, the oscillations in (Formula presented) describing the correlations between the motions of the atoms are accurately reproduced. The neutron effective density of states obtained directly from (Formula presented) yields a good representation of the actual density of states. By introducing a comprehensive scheme, we clarify the relation between neutron and infrared spectra. In particular, we show that the neutron density of states does not distinguish between longitudinal and transverse excitations. Other properties such as the mean-square displacements and the elastic structure factor are also evaluated and found to be in good agreement with experiment.

AB - Using a first-principles approach, we study the vibrational properties of vitreous (Formula presented) which are measured in neutron-scattering experiments. We adopt a model structure consisting of corner-sharing tetrahedra, which was previously generated using first-principles molecular dynamics. We calculate the dynamic structure function (Formula presented) as a function of wave vector (Formula presented) and energy (Formula presented) by taking explicitly into account the correlations between different atoms as given by the normal modes. The effects of temperature and finite displacements are also considered. Overall, the agreement with experiment is very good, as illustrated by the comparison for the density of states. However, the calculated and measured (Formula presented) differ in some cases up to a factor of 2 in absolute intensity. Nevertheless, the oscillations in (Formula presented) describing the correlations between the motions of the atoms are accurately reproduced. The neutron effective density of states obtained directly from (Formula presented) yields a good representation of the actual density of states. By introducing a comprehensive scheme, we clarify the relation between neutron and infrared spectra. In particular, we show that the neutron density of states does not distinguish between longitudinal and transverse excitations. Other properties such as the mean-square displacements and the elastic structure factor are also evaluated and found to be in good agreement with experiment.

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U2 - 10.1103/PhysRevB.57.14133

DO - 10.1103/PhysRevB.57.14133

M3 - Article

AN - SCOPUS:0000861928

SN - 1098-0121

VL - 57

SP - 14133

EP - 14140

JO - Physical Review B - Condensed Matter and Materials Physics

JF - Physical Review B - Condensed Matter and Materials Physics

IS - 22

ER -