9 research outputs found
Low-frequency excitations in glassy selenium: A comparison of neutron-scattering and molecular-dynamics results
The microscopic low-frequency dynamics of glassy selenium is investigated by means of the concurrent use of neutron inelastic scattering and computer simulations. A separation of the dynamic response in terms of intra- and interchain processes is achieved from the analysis of the simulation results. The S(Q,E) dynamic structure factors are analyzed in terms of the frequency moments or from a model scattering law, and the wave-vector dependence of the relevant quantities is established. Finally, the anomalous behavior of the heat capacity at moderately low temperatures is shown to be originated by mostly interchain interactions.Dirección General de Investigación Científica y Técnica PB89-0037-C
Structure and relaxations in liquid and amorphous Selenium
We report a molecular dynamics simulation of selenium, described by a
three-body interaction. The temperatures T_g and T_c and the structural
properties are in agreement with experiment. The mean nearest neighbor
coordination number is 2.1. A small pre-peak at about 1 AA^-1 can be explained
in terms of void correlations. In the intermediate self-scattering function,
i.e. the density fluctuation correlation, classical behavior, alpha- and
beta-regimes, is found. We also observe the plateau in the beta-regime below
T_g. In a second step, we investigated the heterogeneous and/or homogeneous
behavior of the relaxations. At both short and long times the relaxations are
homogeneous (or weakly heterogeneous). In the intermediate time scale, lowering
the temperature increases the heterogeneity. We connect these different domains
to the vibrational (ballistic), beta- and alpha-regimes. We have also shown
that the increase in heterogeneity can be understood in terms of relaxations
Vapour-liquid coexistence in many-body dissipative particle dynamics
Many-body dissipative particle dynamics is constructed to exhibit
vapour-liquid coexistence, with a sharp interface, and a vapour phase of
vanishingly small density. In this form, the model is an unusual example of a
soft-sphere liquid with a potential energy built out of local-density dependent
one-particle self energies. The application to fluid mechanics problems
involving free surfaces is illustrated by simulation of a pendant drop.Comment: 8 pages, 6 figures, revtex
Low-frequency excitations in glassy selenium: A comparison of neutron-scattering and molecular-dynamics results
New techniques for simulating crystals
Methods for simulating solid crystalline phases are generally not as straightforward as those for fluids. This work discusses the reason for this and reviews some recently developed Monte-Carlo techniques for simulating crystalline phases. The self-referential (SR) method for calculating crystal free energies is described first. This technique is particularly straightforward and it is expected to be very versatile. Next, a novel kind of Gibbs ensemble method adapted to treat crystalline solid-fluid coexistence is described. This technique requires free energy calculations of the crystalline phase as input, and of course, these can be provided by the SR method
Correlated atomic motions in glassy selenium
11 págs.; 6 figs.The elastic and total (energy-integrated) structure factors for glassy selenium have been measured by means of neutron spectroscopy within the temperature range 15 KT310 K. The correlated nature of the atomic vibrations gives rise to marked features in the total (energy-integrated) inelastic structure factors defined as the difference between the total and elastic intensities. Also, both structure factors show rather distinct dependences with temperature, which are discussed in some detail. © 1994 The American Physical Society.Work supported in part by Grant No. PB92-0114-C03
(DGICYT, Spain).Peer Reviewe