Structural and dynamical properties of liquid Si: An Orbital-free molecular dynamics study

Abstract

Several static and dynamic properties of liquid silicon near melting have been determined from an orbital free ab-initio molecular dynamics simulation. The calculated static structure is in good agreement with the available X-ray and neutron diffraction data. The dynamical structure shows collective density excitations with an associated dispersion relation which closely follows recent experimental data. It is found that liquid silicon can not sustain the propagation of shear waves which can be related to the power spectrum of the velocity autocorrelation function. Accurate estimates have also been obtained for several transport coefficients. The overall picture is that the dynamic properties have many characteristics of the simple liquid metals although some conspicuous differences have been found.

Covalentlike electronic effects in metallic liquids using an orbital-freeab initiomethod

“…More recently, 12 OF-AIMD studies of liquid Si using 2000 particles have yielded static structural properties in good agreement with both experiment 13,14 and KS-AIMD data, 15 and simulation times were long enough to allow the study of the dynamic structure. Liquid Si has metallic properties, but it is not a typical liquid metal.…”

Pressure-induced structural and dynamical changes in liquid Si—anab initiostudy

“…In illustration, figure 2 shows the OF-AIMD results for the g 3 (θ, r m ) of l-Si and l-Al near their TP's. 9,20 . OF-AIMD results for compressed l-Si are also included in the figure, and a gradual evolution with pressure towards the simple liquid metal distribution is seen.…”

“…We analize the remarkable structural changes occurring between 8 and 14 GPa along with its reflection into several dynamic properties. The intriguing properties of Silicon along with its technological importance have stimulated intensive theoretical 1,2,3,4,5,6,7,8,9 and experimental 10,11,12,13,14,15,16 work. Its high-density forms include the semiconducting and covalent crystalline and amorphous phases and the metallic liquid phase.…”

Collective excitations and viscosity in liquid Bi

“…Parallel to these developments there have been detailed studies of the static, dynamic, and electronic properties of liquids using molecular dynamics (MD) simulations, often with the density functional (DF) theory 6 as the basis of force and energy calculations. These have included studies of Si, 7,8 Ga, 2,9 Mg, 10 Bi, 11,12 Sn, 13 Pb, 14 and Al 15 as well as 58 liquid elements at their triple points (125 atoms in the simulation cell, except for Li, Na, Mg, and Al with 250-384 atoms). 16 The computational demands presented by DF/MD calculations have led to the use of a number of simplifying assumptions.…”

“…A simplification of the standard (Kohn-Sham) DF calculations 6 is provided by "orbital-free" methods, where approximations to the kinetic energy of the non-interacting system are introduced. Simulations with 2000 ions have been performed with this approach in Si (50 ps data collection, 1740 K), 7 Ga (80 ps, three temperatures), 9 and Mg (50 ps, 953 K). 10 Calculations using DF/MD calculations without approximations to the non-interacting kinetic energy have been limited, however, to Sn (64 atoms, 108 ps, three temperatures), 13 Bi (124 atoms, 40 ps, 600 K), 11 and Fe (120 atoms, 40 ps, 1873 K).…”