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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.

The properties of 3He and 4He clusters are investigated in the framework of a density functional approach. We find that 4He clusters are always bound and do not exhibit any shell effect. Conversely, 3He clusters require a minimum number of atoms (Nmin≂30) to ensure binding. 3He clusters are found to exhibit harmonic oscillator type shell effects associated with the magic numbers N=1/3 (m+1)(m+2)(m+3) (with m integer)=40,70,112,168,... and single particle energy gaps of the order of 0.2–0.4 K.

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