Soft Report - Dipartimento di Fisica - Sapienza

Ion Density Fluctuations in Liquid GalliumThe study of ion density fluctuations in the THzrange in metals is a basic branch useful to derivegeneral information on the fluid dynamics. Inaddition, these studies allow to use the ions inmetals as weak probes of the electron fluid responseat low frequency. Indeed, the effective ion-ionpotential is mediated by the electron fluid throughthe dielectric response in a frequency region which isquite small as compared to the Fermi energy, so thatthe electron response can be safely considered asstatic.Despite the long standing research devoted to theanalysis of the electron gas properties, this is still aforefront problem of many body physics.Neutron and photon scattering are the most powerfultools for the investigation of the ion dynamics incondensed systems from crystals to gases.We present here an investigation of the ion dynamicsin liquid Gallium by means of neutron[1] and x-rayscattering[2], as well as, molecular dynamicssimulation[1]. Although liquid alkali metals are theprototype for the study of the electron response,polyvalent metals are also very interesting since theyprovide information on the electron gas at higherdensity than alkali metals, other than additionalinformation on the role of the ion core repulsivepotential. The experimental results of Refs. 1 and 2are summarized in Fig. 1, where the experimentalresults from neutron and x-ray scattering arepresented in comparison to a large scale moleculardynamics simulation. The very good agreementbetween simulation and experiments gives a strongsupport for the ion-ion potential employed in thecomputer experiment. This potential is directlydeduced from the electron gas properties and it isable to reproduce, without adjustable parameters,the experimental results at two quite differenttemperatures. The form we employed is directlydictated from the electron gas response plus arepulsive contribution equal to that used in thestandard Lennard-Jones potential. Therefore theeffective two body potential includes many bodyeffects both the ion liquid and electron liquid throughthe density of the system. In the present simulationthe potential is given by:related to the electron density. The coefficient VRand VF are deduced by comparing the simulated andexperimental structure factors at room temperature.The pair potential proves its effectiveness by beingable to reproduce the static structure factor at hightemperature (970 K) without adjustable parameters.In addition the simulation is quite effective inproviding a good agreement with the experimentalresults for the dynamic structure factor as measuredat room temperature and 970 K by neutronscattering and at room temperature by x-rayscattering.References[1] L. E. Bove, F. Formisano, F. Sacchetti, C. Petrillo,A. Ivanov, B. Dorner, and F. Barocchi, Phys. Rev.B71, 014207 (2005).[2] T. Scopigno, A. Filipponi, M. Krisch, G. Monaco,G. Ruocco, and F. Sette, Phys. Rev. Lett. 89, 255506(2002).AuthorsL. E. Bove,1 F. Formisano, C. Petrillo, F. SacchettiDipartimento di Fisica, Università di Perugia, CRS-SOFT Unità di Perugia and Centro per i MaterialiInnovativi e Nanostrutturati (CEMIN), Via A. Pascoli,I-06123 Perugia, Italy.99SOFT Scientific Report 2004-06