Ca impurity in small mixed $^4$He-$^3$He clusters

TL;DR

This study investigates the position and spectral properties of calcium impurities in small mixed helium clusters using diffusion Monte Carlo simulations, revealing their location preferences and spectral shifts.

Contribution

It provides new insights into calcium impurity behavior in small mixed helium clusters, including their preferred positions and spectral shifts, complementing previous large-cluster studies.

Findings

Calcium sits at the $^4$He-$^3$He interface.

In $^4$He clusters, Ca forms a deep surface dimple.

In $^3$He clusters, Ca becomes fully solvated.

Abstract

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 $^4$He-$^3$He 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 $^4$He clusters, and to become fully solvated for $^3$He clusters. We have calculated the absorption spectrum of Ca around the $4s4p \leftarrow 4s^2$ 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.