Singly and doubly lithium doped silicon clusters: Geometrical and electronic structures and ionization energies

The geometric structures of neutral and cationic SinLim0/+ clusters with n = 2-11 and m = 1, 2 are investigated using combined experimental and computational methods. The adiabatic ionization energy and vertical ionization energy (VIE) of SinLim clusters are determined using quantum chemical methods (B3LYP/6-311+G(d), G3B3, and CCSD(T)/aug-cc-pVxZ with x = D, T), whereas experimental values are derived from threshold photoionization experiments in the 4.68-6.24 eV range. Among the investigated cluster sizes, only Si6Li2, Si7Li, Si10Li, and Si11Li have ionization thresholds below 6.24 eV and could be measured accurately. The ionization threshold and VIE obtained from the experimental photoionization efficiency curves agree well with the computed values. The growth mechanism of the lithium doped silicon clusters follows some simple rules: (1) neutral singly doped SinLi clusters favor the Li atom addition on an edge or a face of the structure of the corresponding Si-n(-) anion, while the cationic SinLi+ binds with one Si atom of the bare Si-n cluster or adds on one of its edges, and (2) for doubly doped SinLi20/+ clusters, the neutrals have the shape of the Sin+1 counterparts with an additional Li atom added on an edge or a face of it, while the cations have both Li atoms added on edges or faces of the Si-n(-) clusters. (C) 2012 American Institute of Physics. [doi:10.1063/1.3672164]