Diffusion Monte Carlo investigation of electronic structure properties for 13-atom alkali metal clusters

Electronic structure properties of 13-atom icosahedral alkali metal clusters (X 13, X = Li, Na, K, Rb, and Cs) were investigated with the Diffusion Monte Carlo (DMC) and Density Functional Theory (DFT) methods. The overall results of vertical ionization energies, vertical electron affinities and dissociation energies are in good agreement with theoretical/experimental values found in the literature for these clusters. However, the DFT approach investigated, B3LYP, provides larger discrepancies than DMC for dissociation energies. In this case, empirical dispersion corrections seem important to improve the binding energy data from DFT. We also considered heteronuclear alkali metal clusters such as YX 12, where the Y atom was placed at the center and also at the face of the initial icosahedral structure of X 13. To our knowledge, the results for such heteronuclear clusters are being reported for the first time, providing an important initial step for understanding these systems. This work demonstrates that face-type YX 12 clusters are usually more strongly bonded than the respective center-type structures, except for LiNa 12, CsRb 12, and KCs 12 (according to DMC results). In addition, the trends evidenced in binding energies are analysed in details.