Microscopic dynamics in the liquid Li-Na alloy: An ab initio molecular dynamics study

We present results for several structural and dynamical properties of the liquid ${\mathrm{Li}}_{1-x}{\mathrm{Na}}_x$ alloy. The study has been carried out by means of the orbital-free ab initio molecular dynamics method, combined with local ionic pseudopotentials constructed within the same framework. We obtain good agreement with the available experimental data, reproducing accurately, the strong homocoordinating tendencies exhibited by this alloy. The calculated partial dynamic structure factors exhibit clear side peaks whose frequencies, for $q<~0.25{\AA }^{-1},$ correspond to the hydrodynamic sound dispersion of the binary alloy, whereas for larger q values fast and slow sound modes are identified. The mass ratio in this system, $m_{\mathrm{Na}}{/m}_{\mathrm{Li}}\approx 3,$ is the smallest one so far for which the fast mode is observed.