Structural and dynamical properties of superfluid helium: A density-functional approach

We present a density functional for liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, 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 superfluid 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 backflow effects, is discussed. The spectrum of the elementary excitations of the free surface and films is studied.