Dynamic structure in a molten binary alloy by ab initio molecular dynamics: Crossover from hydrodynamics to the microscopic regime

¹ Departamento de Física Teórica, Universidad de Valladolid - 47011 Valladolid, Spain
² Department of Physics, Queen's University - Kingston, K7L 3N6 Ontario, Canada

Received: 15 November 2002
Accepted: 23 January 2003

Abstract

The dynamic structure factor of the liquid alloy at T=590 has been calculated by ab initio molecular-dynamics simulations using 2000 particles. For small wave vectors, , we find clear side peaks in the partial dynamic structure factors. Whereas for the peak frequencies correspond to the hydrodynamic sound dispersion of the binary alloy, for greater q-values we obtain two modes with phase velocities above and below the hydrodynamic sound. A smooth transition between hydrodynamic sound and the two collective modes is shown to take place in the range . The mass ratio in this system, , is the smallest one so far for which the fast mode is observed. We also predict that inelastic X-ray scattering experiments would be able to detect the slow mode, and explain why the inelastic neutron scattering measurements (GARTRELL-MILLS P. R. et al., Physica B, 154 (1988) 1) do not show any of these modes.