Structural and dynamical properties of liquid Mg. An orbital-free molecular dynamics study

Abstract

Several static and dynamic properties of liquid magnesium near melting have been evaluated by the orbital-free ab initio molecular dynamics method. The calculated static structure shows good agreement with recent experimental data, including an asymmetric second peak in the structure factor which has been linked to the existence of an important icosahedral short-range order in the liquid. As for the dynamic structure, we obtain collective density excitations with an associated dispersion relation which closely follows recent experimental results. Accurate estimates have also been obtained for several transport coefficients.

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.…”

“…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). 17 In addition to having a larger fraction of atoms close a) Electronic mail: r.jones@fz-juelich.de to a neighboring cell (larger "finite size effects"), small simulation cells mean that the lowest wave-vector that can be considered (2π/L for a cubic cell of side L) is correspondingly larger.…”

Hidden scale invariance of metals

“…Fig. 6 compares the experimentally determined structure factor S(q) of Mg at the triple point [72][73][74] with that of the IPL model (without using any free parameters). The agreement is excellent.…”

Generalised hydrodynamic description of the time correlation functions of liquid metals:ab initiomolecular dynamics study

“…In the ab initio study of liquid boron [19] a fitting scheme for S(k, ω) based on the second-order memory function (MF) approach was applied. Another kind of a fitting scheme was used in ab initio studies of collective dynamics of liquid Sn [20], Hg [21], Mg [22], Bi [23]. The AIMD-derived density-density time correlation functions F nn (k, t) were fitted to an analytical ansatz containing a few k-dependent fitting parameters.…”

“…In [20,21] the analytical ansatz for F nn (k, t) was a hydrodynamic-type expression [1,2] with k-dependent weights of relaxing and oscillating contributions, that did not allow to study explicitly effects of non-hydrodynamic processes like structural relaxation. More correct fitting expressions for F nn (k, t) with a few exponential contributions were applied to analysis of the AIMD-derived density-density time correlation functions in [22] and [23]. However only in [23] the dispersion of collective excitations was associated with the k-dependence of the frequency (as a fitting parameter) of oscillating contribution to F nn (k, t), while in other ab initio studies the fit was used either for analysis of slow and fast decay channels in the memory function or for obtaining the smooth replica of F nn (k, t) with subsequent its analytical time Fourier transformation and estimation of peak positions of corresponding S(k, ω) or C L (k, ω).…”