Pseudopotential effects in alkali clusters by the pseudo-Hamiltonian technique

Using the pseudo-Hamiltonian technique we investigate nonlocal ion-pseudopotential effects on the dipole strength distribution and the electronic shell structure of alkali clusters. The results obtained for sodium clusters are compared with the predictions of the standard jellium model (JM) and of models involving reasonable local pseudopotential parametrizations. Some wrong JM predictions—shift of some low magic sizes, insufficient redshift of the surface plasmon frequency relative to the Mie frequency—are corrected, but a noticeable discrepancy remains with regard to the supershell structure. We also provide explicit formulas allowing us to take into account the nonlocal pseudopotential effects in standard JM Kohn-Sham codes very easily, without involving a change of the computational method or time. In the second part of this paper we restore the reliability of the pseudo-Hamiltonian approximation, on which some doubts have been recently cast, because of incorrect predictions concerning the bulk properties of lithium. From a careful analysis of the nonlocal effects in the case of a smoothed ionic background, we show that a specific pseudo-Hamiltonian parametrization has to be systematically selected for ensuring maximum accuracy. We successfully test the suitability of this parametrization in the case of lithium clusters, through a comparison with recently published results obtained in using accurate norm-conserving nonlocal pseudopotentials. © 1996 The American Physical Society.