Equilibrium properties of simple metal thin films in the self-compressed stabilized jellium model

Abstract

In this work, we have applied the self-compressed stabilized jellium model to predict the equilibrium properties of isolated thin Al, Na, and Cs slabs. To make a direct correspondence to atomic slabs, we have considered only those $L$ values that correspond to $n$-layered atomic slabs with $2\le n\le 20$, for surface indices (100), (110), and (111). The calculations are based on the density functional theory and self-consistent solution of the Kohn-Sham equations in the local density approximation. Our results show that firstly, the quantum size effects are significant for slabs with sizes smaller or near to the Fermi wavelength of the valence electrons $\lambda_{\rm F}$, and secondly, some slabs expand while others contract with respect to the bulk spacings. Based on the results, we propose a criterion for realization of significant quantum size effects that lead to expansion of some thin slabs. For more justification of the criterion, we have tested on Li slabs for $2\le n\le 6$. We have compared our Al results with those obtained from using all-electron or pseudo-potential first principles calculations. This comparison shows excellent agreements for Al(100) work functions, and qualitatively good agreements for the other work functions and surface energies. These agreements justify the way we have used the self-compressed stabilized jellium model for the correct description of the properties of the simple-metal slab systems. On the other hand, our results for the work functions and surface energies of large-$n$ slabs are in good agreement with those obtained from applying the stabilized jellium model for semi-infinite systems. Moreover, we have performed the slab calculations in the presence of surface corrugation for a selected Al slabs and have shown that the results are worsened.