Atomic structure and collective excitations of medium size NanKm clusters

Abstract

Abstract. Density functional theory is used to study the atomic and electronic structure of NanK m clusters with up to seventy atoms. The simplifying approximation has been made of replacing the external potential of the ionic background by its spherical average about the cluster centre in the iterative process of solving the Kohn-Sham equations for each geometry tested. The search for the equilibrium geometry is performed by employing steepest descent and simulated annealing techniques. We have found segregation of K to the surface and when the cluster is large enough, a neat stratification of K and Na shells. Those effects (segregation and stratification) do not perturb the electronic magic numbers well known for pure alkali metal clusters. Our results for the atomic structure are rather similar to those reported earlier for NanCsn clusters. We have also studied in a selected case, Naz0Cs20 , the dependence of the collective electronic excitation spectrum on the segregation and other geometric characteristics of the cluster.

Single-component surface in binary self-assembled NaK nanoalloy clusters

“…This corresponds to an alloy of approximately Na 0.44 K 0.56 composition in the core. The mixed NaK clusters produced with lower Na/K vapor ratio thus consist of an alloy core with approximately equal amounts of Na and K, surrounded by a layer of K. This structure is consistent with the predictions for small, mixed Na 0.5 K 0.5 clusters, 4 and liquid K-rich alloys, 3 whereas liquid alloys of the observed composition have been predicted to have a surface with a small but non-negligible Na fraction. 2 For increasingly Na-rich macroscopic alloys, theory indicates a gradually decreasing K surface dominance.…”

“…We conclude that the whole process allows sufficient intracluster diffusion to form the low-energy structures similar to those theoretically suggested-before the temperature gets too low. 4 Concluding, we can state that, in the self-assembling gasaggregation process of binary nanoalloy formation out of the mixed-vapor phase of Na and K, the element with the lower surface energy, K, occupies the surface sites. The surface segregation in the system makes Na practically absent on the surface, even when K is the minority species in the alloy core.…”

“…2 On the opposite side of the dimensional scale, calculations using density-functional theory predict NaK clusters of equal Na/K proportions consisting of tens of atoms to have ground-state structures at 0 K with a strongly K-dominated surface. 4 None of these theoretical predictions have to the best of our knowledge been tested experimentally. We will here present an experimental study of NaK nanoalloy clusters produced by gas aggregation.…”

Ab initio structures and polarizabilities of sodium clusters

“…Many authors, using models of various sophistication levels, have attempted to determine ground state structures. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Unfortunately, cluster structures are generally not amenable to direct experimental determination. Thus, it is customary to test the obtained structures indirectly, by computing an experimentally accessible quantity that depends on structural properties.…”

Structure and energetics of equiatomic K–Cs and Rb–Cs binary clusters

“…López et al [35][36][37] studied the structural and segregation properties of Na-Cs, Na-Li, and Na-K nanoalloys using the density functional theory method. Ab initio calculations, such as those of Deshpande et al 38,39 on Na-Li clusters, are restricted to small sizes up to N = 12.…”