Limiting properties of (MgO)(n) and (CaO)(n) clusters

The limiting behaviours of bond distances and binding energies are studied for small alkaline earth oxide clusters, employing the B3LYP density functi onal. Validation of the applicability of density functional theory is made on selected clusters by MP4 calculations. Basis set effects on cluster stru ctures and binding energies are determined, and comparisons between (MgO)(1 -16) and (CaO)(1-12) are made. For CaO, the need to include at least two d- polarisation functions for a proper description of the cluster binding ener gy is emphasised. Consistency in limiting binding energies for monolayers o f MgO and CaO, determined here to be 8.3 eV and 9.2 eV respectively, in con junction with MP4 calculations on (MgO)(4), is employed to critically reass ess claimed converged bulk binding energies for small cube-like MgO cluster s.