Fast sound in liquid water

Wavevector- and frequency-dependent shear viscosity of water: the modified collective mode approach and molecular dynamics calculations

“…For this reason, these quantities should be treated as quasivariables. Using set (8), one constructs the matrix…”

“…The nonequilibrium properties of water have been extensively studied during the last three decades by means of experiment [1], molecular dynamics (MD) simulations [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], different versions of the collective mode approach [4,10,11,14,[19][20][21], modecoupling theory [22], and others. As a result, it has been established that there are several primary types of collective excitations in the spectra of time correlation functions of liquid water [1][2][3][5][6][7][8][10][11][12]14,20,21].…”

“…As a result, it has been established that there are several primary types of collective excitations in the spectra of time correlation functions of liquid water [1][2][3][5][6][7][8][10][11][12]14,20,21]. They are related to the extended hydrodynamic sound, heat, and diffusive modes, which originate from the center-ofmass motions of constituent molecules, and the kinetic optical-like modes coming from the rotational (librational) motions.…”

Inelastic X-Ray Scattering: Great Potential Demonstrated

“…The new results strongly favour theore tical models for the dynamics of water which account for fast sound in terms of an anomalously large increase at high frequen cies of the speed of propagation of collec tive acoustic-like excitations [4,5]. The phy sical origin of this increase lies mostly in the interplay between the different contributions to the intermolecular potential, i.e., the different roles played by electrostatic and Lennard-Jones-like terms in determining the intermolecular distances and the q-w depen dence of the molecular dynamics [5].…”

“…Since then, many theoretical analyses and molecular dynamics simulations have tried to clarify the origin of these excitations [3][4][5]. Despite these efforts, the issue could not be settled, mainly because neutron data were only available for a limited region of momentum transfer -frequency (q-w) space.…”