Collective excitations in molten iron above the melting point: A generalized collective-mode analysis of simulations with embedded-atom potentials

摘要

It is shown, that the embedded-atom potential nicely describing structural properties of high pressure Fe [A. B. Belonoshko et al, Phys. Rev. Lett. 84, 3638 (2000)] can be successfully used for description of collective dynamics of liquid iron. A combination of molecular dynamics simulations and a fit-free analysis based on the approach of generalized collective modes (GCM) is used for calculations of spectra of collective excitations and relaxing modes at 1843 K. The obtained spectrum of acoustic excitations in the long-wavelength region perfectly agrees with the experimental speed of sound and reproduces the dispersion estimated from inelastic X-ray scattering (IXS) experiments [S. Hosokawa et al, Phys. Rev. B 77, 174203 (2008)]. Heat fluctuations in liquid Fe were studied and resulted in calculated ratio of specific heats y ≈ 1.40 being in agreement with the IXS-experiment estimate. We report analysis of the wave-number dependence of relaxation processes and their contributions to dynamic structure factors. This permits estimation of most important relaxation processes contributing to the shape of dynamic structure factors of liquid Fe in different regions of wave numbers.