Potential functions and static and dynamic properties of Mgm+Arn, (m=1, 2; n=1-18) clusters

Analytical potential functions have been constructed for (MgArn)-Ar-m+, m=1, 2, clusters by combining ab initio calculations with the electrostatic model of ion-induced dipole and induced dipole-induced dipole interactions. The most stable structures and dynamic properties are investigated by molecular dynamics techniques. For Mg+Ar12 an icosahedral geometry is predicted. For Mg+Arn clusters with n = 7-12 two series of minima with small difference's in energy were found; in one the magnesium ion stays inside the cluster (solvated) and in the other on the surface of the system. For n > 9, clusters with Mg on the surface are slightly more stable and have a distinguishable high vibrational frequency relative to those with the magnesium ion inside. We find no such trends for Mg2+Arn clusters, in which the Mg cation is always solvated. The absolute minimum of Mg2+Ar4 is a regular tetrahedron, and that of Mg2+Ar6, a regular octahedron. The stability of all these clusters is investigated by studying caloric curves, root mean square bond length fluctuations, radial distributions, and power spectra.