Density functional calculations for 4He droplets

TL;DR

This paper introduces a new density functional tailored for helium droplets, accurately predicting their static and dynamic properties, including oscillations and excitation spectra, by incorporating effects like backflow.

Contribution

A novel density functional that accurately models helium droplets' properties, including static response and excitation spectra, with explicit connection to liquid structure.

Findings

Static density profiles show significant oscillations.

Evaporation energy deviates from classical liquid drop behavior for small droplets.

Functional predicts excitation spectrum in the roton wavelength range.

Abstract

A novel density functional, which accounts correctly for the equation of state, the static response function and the phonon-roton dispersion in bulk liquid helium, is used to predict static and dynamic properties of helium droplets. The static density profile is found to exhibit significant oscillations, which are accompanied by deviations of the evaporation energy from a liquid drop behaviour in the case of small droplets. The connection between such oscillations and the structure of the static response function in the liquid is explicitly discussed. The energy and the wave function of excited states are then calculated in the framework of time dependent density functional theory. The new functional, which contains backflow-like effects, is expected to yield quantitatively correct predictions for the excitation spectrum also in the roton wave-length range.