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 -