Density-functional calculations of excitations in doped helium nanodroplets

Time-dependent density-functional theory is used to explore the microscopic dynamics of superfluid helium. The framework of normal modes in density-functional theory is derived, along with formulae for interpreting its results.; Numerical calculations are presented for spherically symmetric systems. These results are the first published calculations of helium excitations with high angular momenta, which are essential for determining the structure factor and superfluid fraction of helium nanodroplets with density-functional theory. The helium density functional of Dalfovo et al., Phys. Rev. B. 52,2 p. 1193 (1995) is used, and a list of quantitative and qualitative future improvements is presented.; The surface waves of helium nanodroplets are calculated beyond the simple liquid-drop model. We find that there are three separate branches of surface waves, not only one as previously assumed throughout the literature.; For doped superfluid helium droplets, localized excitations in the solvation density are calculated, and their influence on dopant spectra is explored and compared to experimental results. The split zero-phonon lines of electronic dopant spectra are due to local conformers of strongly attached helium shells, which spontaneously break the spherical symmetry of the system. The structures on the phonon wings of such spectra are related to localized helium excitations. The influence of helium excitations on the rotational dynamics of linear molecules is studied for HCN/DCN and HCCH, and is linked to a permanent normal-fluid fraction induced by the anisotropy of the molecules.; The global and local normal-fluid fractions of pure and doped superfluid helium nanodroplets are calculated and compared to previous results.