  The Unitary Correlation Operator Method (UCOM) is employed to treat
short-range correlations in both, homogeneous liquid and small droplets of
bosonic He-4 atoms. The dominating short-range correlations in these systems
are described by an unitary transformation in the two-body relative coordinate,
applied either to the many-body state or to the Hamiltonian and other
operators. It is shown that the two-body correlated interaction can describe
the binding energy of clusters of up to 6 atoms very well, the numerical effort
consisting only in calculating one two-body matrix element with Gaussian
single-particle states. The increasing density of bigger droplets requires the
inclusion of correlation effects beyond the two-body order, which are
successfully implemented by a density-dependent two-body correlator. With only
one adjusted parameter the binding energies and radii of larger droplets and
the equation of state of the homogeneous He-4 liquid can be described
quantitatively in a physically intuitive and numerically simple way.
