We present a density functional for liquid He, properly accounting for the static response function and the phonon-roton dispersion in the uniform liquid. The functional is used to study both structural and dynamical properties of superIIIuid helium in various geometries. The equilibrium properties of the free surface, droplets, and films at zero temperature are calculated. Our predictions agree closely with the results of ab initio Monte Carlo calculations, when available. The introduction of a phenomenological velocity-dependent interaction, which accounts for back6ow effects, is discussed. The spectrum of the elementary excitations of the free surface and films is studied.

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The probability of evaporation induced by R + and R − rotons at the surface of superfluid helium is calculated using time dependent density functional theory. We consider excitation energies and incident angles such that phonons do not take part in the scattering process. We predict sizable evaporation rates, which originate entirely from quantum effects. Results for the atomic reflectivity and for the probability of the roton change-mode reflection are also presented.PACS number: 67.40.Db Typeset using REVT E X 1

A detailed study of the dispersion law of surface excitations in liquid 4 He at zero temperature is presented, with special emphasis to the short wave length region. The hybridization mechanism between surface and bulk modes is discussed on a general basis, investigating the scattering of slow rotons from the surface. An accurate density functional, accounting for backflow effects, is then used to determine the dispersion of both bulk and surface excitations.The numerical results are close to the experimental data obtained on thick films and explicitly reveal the occurrence of important hybridization effects between ripplons and rotons. 67.40Typeset using REVT E X