Collective excitations in liquid : Neutron scattering and molecular-dynamics simulationsE. Guarini1, U. Bafile2, F. Barocchi3, 1, F. Demmel4, F. Formisano5, M. Sampoli6, 1 and G. Venturi3, 1
1 CNR-INFM and CRS Soft, c/o Dipartimento di Fisica, Università di Firenze I-50019 Sesto Fiorentino, Italy
2 CNR-ISC, Sezione di Firenze - I-50019 Sesto Fiorentino, Italy
3 Dipartimento di Fisica, Università di Firenze - I-50019 Sesto Fiorentino, Italy
4 ISIS Facility, Rutherford Appleton Laboratory - Chilton, Oxfordshire, OX11 0QX, UK
5 CNR-INFM and CRS Soft, c/o Institut Laue Langevin - BP 156, Grenoble, France
6 Dipartimento di Energetica, Università di Firenze - I-50139 Firenze, Italy
received 18 July 2005; accepted in final form 13 October 2005
published online 4 November 2005
We have investigated the dynamic structure factor of liquid at in the wave vector range by means of neutron scattering and molecular-dynamics simulation, in order to study the centre-of-mass collective dynamics. The agreement between the experimental spectra and those simulated using a recent ab initio based intermolecular potential is good, particularly at low Q. Underdamped collective excitations, detected in the whole experimental Q-range, characterize the dynamics of liquid as markedly different from that of other molecular liquids. Also, the energy and damping of collective excitations in methane are shown to differ considerably, even at the lowest measured Q-values, from those of linearized hydrodynamic modes. An empirical relation, able to reconcile the different wave vector ranges of mode propagation observed in disparate liquids, is investigated.
61.12.Ex - Neutron scattering (including small-angle scattering).
61.25.Em - Molecular liquids.
61.20.Ja - Computer simulation of liquid structure.
© EDP Sciences 2005