Ab initio study of collective excitations in a disparate mass molten salt

Abstract

Ab initio molecular dynamics simulations and the approach of generalized collective modes are applied for calculations of spectra of longitudinal and transverse collective excitations in molten LiBr. Dispersion and damping of low- and high-frequency branches of collective excitations as well as wave-number dependent relaxing modes were calculated. The main mode contributions to partial, total, and concentration dynamic structure factors were estimated in a wide region of wave numbers. A role of polarization effects is discussed from comparison of mode contributions to concentration dynamic structure factors calculated for molten LiBr from ab initio and classical rigid ion simulations.

Ab initio study of electron-ion structure factors in binary liquids with different types of chemical bonding

“…The partial electron-ion structure factors show similar extrema with different signs at k C , supporting the finding that the cation, having less-than-average screening electrons, corresponds to the negative minimum of S el−Rb (k) at k ∼ k C , and anion -to the positive maximum of S el−F (k). Note that this seems to be the general behaviour of the partial electron-ion structure factors in the region of the main peak of concentration (charge) structure factor S CC (k), observed previously in molten LiBr 25 and CsAu. 26 Concerning the density fluctuations, similarly as for liquid metallic alloy both partial electron-ion structure factors show positive extrema at k ∼ k N .…”

“…Ab initio simulations focused on electron-ion correlations were reported for pure liquid Mg and Bi, 19 metallic H, 20 Na, Mg, and Al, 21 high-pressure molten Li. 22 For binary liquids though we were able to find only a few studies on liquid GeSe 4 , 23 SiO 2 , SiSe 2 , and GeSe 2 , 24 and there were recently also our simulation results for molten salt LiBr 25 and liquid equimolar alloy CsAu. 26 Binary A-B liquids or solids essentially differ from the pure components from the point of view of local electroneutrality and electron density distribution.…”

Effect of ion polarization on longitudinal excitations in ionic melts

“…Taking into account the fact that for the melts of interest ϕ 2 q /ω 2 0 ≪ 1 19,20,29 , we obtain a simple expression for the optic modes…”

“…Thus, taking into account polarization processes we approximate the frequency of optic modes to the value obtained from AI MD, which is about 61 ps −1 (see Ref. 20 ). We also observe a small increase of the damping coefficient from 10 ps −1 in RI model to 11 ps −1 within the considered model.…”

“…If the value of high-frequency dielectric permittivity ε is about 2 or higher the polarization effects are essential, whereas for the rigid-ion model ε = 1. In the works 17,20 it was shown that the polarization processes lead to a sufficient redistribution of the contributions from collective modes to concentration dynamic structure factor. Herewith, the contribution from the relaxation mode related with the conductivity of the system increases whereas the one from optic modes decreases in comparison with the rigid-ion model.…”