The structure of small mixed helium clusters doped with one calcium atom has
been determined within the diffusion Monte Carlo framework. The results show
that the calcium atom sits at the 4He-3He interface. This is in agreement
with previous studies, both experimental and theoretical, performed for large
clusters. A comparison between the results obtained for the largest cluster we
have considered for each isotope shows a clear tendency of the Ca atom to
reside in a deep dimple at the surface of the cluster for 4He clusters, and
to become fully solvated for 3He clusters. We have calculated the absorption
spectrum of Ca around the 4s4p←4s2 transition and have found that
it is blue-shifted from that of the free-atom transition by an amount that
depends on the size and composition of the cluster.Comment: 24 pages, 11 figures. Accepted on Journal of Chemical Physic