The structures of an isolated CAl12 cluster and a solid composed of CAl12 clusters have been studied using the Car-Parrinello method, based on the density functional theory and the local density approximation. We have compared the results of using the ultrasoft Vanderbilt pseudopotential with those of both a traditional pseudopotential and a linear combination of atomic orbitals method. We have confirmed the high stability of the cluster in its icosahedral structure. However, we show that the cluster-assembled solid is unstable against melting of the clusters, as previously found for SiAl12.