Structural evolution and stabilities of neutral and anionic clusters of lead sulfide: Joint anion photoelectron and computational studies

Abstract

The geometric and electronic structures of both neutral and negatively charged lead sulfide clusters, (PbS)(n)/(PbS)(n)(-) (n = 2-10) were investigated in a combined anion photoelectron spectroscopy and computational study. Photoelectron spectra provided vertical detachment energies (VDEs) for the cluster anions and estimates of electron affinities (EA) for their neutral cluster counterparts, revealing a pattern of alternating EA and VDE values in which even n clusters exhibited lower EA and VDE values than odd n clusters up until n = 8. Computations found neutral lead sulfide clusters with even n to be thermodynamically more stable than their immediate (odd n) neighbors, with a consistent pattern also being found in their HOMO-LUMO gaps. Analysis of neutral cluster dissociation energies found the Pb(4)S(4) cube to be the preferred product of the queried fragmentation processes, consistent with our finding that the lead sulfide tetramer exhibits enhanced stability; it is a magic number species. Beyond n = 10, computational studies showed that neutral (PbS)(n) clusters in the size range, n = 11-15, prefer two-dimensional stacking of face-sharing lead sulfide cubical units, where lead and sulfur atoms possess a maximum of five-fold coordination. The preference for six-fold coordination, which is observed in the bulk, was not observed at these cluster sizes. Taken together, the results show a preference for the formation of slightly distorted, fused cuboids among small lead sulfide clusters.

(PbS)32: A baby crystal

“…The accuracy of this method has been established in our previous study. 6 For larger, composite clusters that contain multiple (PbS) 32 units, Gaussian-based calculations are prohibitively expensive, and thus for these, we have used the DMOL3 program suite. 11 For these clusters, the PW91 functional, 12 along with the Double Numerical plus d-functions (DND) and Density functional Semi-core PseudoPotentials (DSPP) basis sets, 13 were used.…”

“…[1][2][3][4] While most studies have focused on colloidal nanoparticles of lead sulfide, 5 work on isolated (gas phase) clusters of lead sulfide, (PbS) n , has been relatively scarce. Recently, in a combined experimental and theoretical study 6 we explored the geometric structures and electron affinities of gas-phase lead sulfide clusters, (PbS) n , ranging in size from n = 1-15. With its large highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap and as the preferred product of cluster fragmentation, (PbS) 4 was shown to be the most stable of the lead sulfide clusters studied.…”

Size Selected Clusters on Surfaces

“…[23] To set the stage for the STM studies of "baby crystals," our previous work combined both experiments and theory to explore the geometric structures and electron affinities of small, gas-phase, lead sulfide clusters, (PbS) n , ranging in size from n = 2-15. [25] First, photoelectron spectroscopy was conducted on size-selected cluster anions to acquire both ground and excited state electronic structure information as well as the electron affinity values of the cluster anions' neutral counterparts. Figure 4 and Figure 5 display the calculated geometric structures of neutral and anionic (PbS) n clusters with n=1-10, respectively.…”

Size effect on the structural and electronic properties of lead telluride clusters

“…This can also be seen from the second‐order energy difference and binding energy graph, that is, a magic number species. A magic cluster is usually described by outstandingly high stability compared to its instantaneous neighbors, a large HL gap, and binding energy than that of its instant neighbors. In addition, it is obvious from the graph that as the cluster size increases, the energy required to fragment PbTe, (PbTe) 2 , and (PbTe) 4 clusters from (PbTe) n clusters increases, on the average.…”