Ab InitioSimulations for the Ion-Ion Structure Factor of Warm Dense Aluminum

Abstract

We perform ab initio simulations based on finite-temperature density functional theory in order to determine the static and dynamic ion-ion structure factor in aluminum. We calculate the dynamic structure factor via the intermediate scattering function and extract the dispersion relation for the collective excitations. The results are compared with available experimental x-ray scattering data. Very good agreement is obtained for the liquid metal domain. In addition we perform simulations for warm dense aluminum in order to obtain the ion dynamics in this strongly correlated quantum regime. We determine the sound velocity for both liquid and warm dense aluminum which can be checked experimentally using narrow-bandwidth free electron laser radiation.

Ab initiosimulations of the dynamic ion structure factor of warm dense lithium

“…However, for all scattering angles the calculated central mode seems to be lower and broader compared to the experiment. This feature has been observed before [42]. In future work the DSF can be used to determine more material properties from the hydrodynamic model [19,43,44] or an extended hydrodynamic model [45] and in this sense check a possible influences of the used thermostat [46], which has to be further benchmarked; i.e.…”

Evidence for out-of-equilibrium states in warm dense matter probed by x-ray Thomson scattering

“…In OB method, electrons are separated into valence and core electrons, that are frozen in the pseudopotential while in OF method, the electrons all interact with the external potential. These frozen-core electrons were suspected by Rüter and Redmer [10] to be the origin of the failure of OB simulations to reproduce the data. However, we find that OF simulations at equilibrium (T i = T e = 10 eV), in which all electrons interact with the potential, also do not agree with the experimental results.…”

“…The interpretation of this experiment has been recently extended to ab initio quantum molecular dynamics simulations in the Kohn-Sham ansatz [10]. These simulations performed under equilibrium conditions (8.1 g/cm 3 , 10 eV) do not reproduce the intensity of the ion feature as well as the corresponding ion structure factor.…”

“…f I (k) is known as the ion form factor and q(k) as the screening density, the sum of which defines the atomic form factor. Rüter and Redmer [10] have used Hubbell's tabulated atomic form factor for isolated atoms at zero temperature [24]. Since these tables are computed at zero temperature, it seemed to us preferable to recompute the atomic form factor within the Finite temperature TF average atom model.…”

“…For electronic temperatures of 10 eV and densities of order of 1-3 times the normal density, the only solution to get acceptable OB simulation times is to reduce the number of atoms and hence the number of orbitals. For the conditions in Al, OB simulations were performed with 64 ions [10]. This limitation is overcome by OF methods that can handle hundreds of ions (here 432) for the same computational cost with only a small loss of accuracy compared to the OB results.…”