Comprehensive understanding of size‐, shape‐, and composition‐dependent polarizabilities of Si_mC_n (m, n = 1–4) clusters

Abstract

We performed a comprehensive study of the size-, shape-, and composition-dependent polarizabilities of Si m C n (m, n = 1-4) clusters on the basis of the density-functional-based coupled perturbed Hartree-Fock calculations. We found better correlations between the polarizabilities and both the binding energies (E b ) and change in charge distribution (∆q) than the energy gaps (E g ). The α values exhibit overall decreasing and increasing trends with increases in the E b and ∆q values, respectively. For isomers with the same E b values and different polarizabilities, ∆q can well explain the difference in polarizabilities. The π-electron delocalization effect is the best factor for understanding the shape-dependence. For a given m/n value, the linear clusters have an obviously larger polarizability than both the prolate and compact clusters, irrespective of the cluster size. We fit a quantitative expression [α = A -(A -B) × exp(-k(m/n))] to describe the composition-dependent polarizabilities.Keywords: Binding energy, energy gap, charge distribution, polarizability, silicon carbide cluster IntroductionIn the last 20 years, the (hyper)polarizabilities of small semiconductor clusters such as gallium arsenide (GaAs), silicon (Si), silicon carbide (SiC), and aluminum phosphide (AlP) clusters have attracted much attention . Experimental studies have shown that the static polarizabilities of Si m (m = 9-50) and Ga m As n (m + n = 5-30) clusters fluctuate around their corresponding bulk values [12]. These experimental results have motivated many theoretical studies of the polarizabilities of Si and GaAs clusters [1, 2, 4, 6 -9, 16, 26, 27]. Theoretical studies have shown that the size of the polarizability directly or indirectly depends on various factors such as the cluster size, cluster shape, cluster composition, energy gap, binding energy, ionization potential, and so on. The size-dependence of the polarizabilities has been well known for Si and GaAs clusters. For small Si m (m < 10) and Ga n As m (n + m < 8) clusters, the theoretical polarizabilities are higher than the bulk value and decrease with an increase in cluster size [1,2,9,12,16], as indicated by the number of atoms in a cluster. For mediate-size Si m (m = 9-50) and

Searching for Stable SinCn Clusters: Combination of Stochastic Potential Surface Search and Pseudopotential Plane-Wave Car-Parinello Simulated Annealing Simulations

“…This trans isomer has a corresponding cis isomer, labeled as 1c in Figure 1 having energy 0.09 eV higher. This isomer cluster has been studied previously by different groups [13,14,15,16,17,18] and various stable structures were reported as lowest energy structures. The low lying energy structures we found with our search method include previously published structures, labeled as 1b , 1d , 1f and 1g in Figure 1.…”

“…The structures and relative energies (in eV) of the lower energy Si 4 C 4 clusters. Structures labeled in red have been previously reported in literature as 1b [13], 1d [14,15,16], 1e [17], 1f [17], 1g [18]. …”

Electrostatic screening mediated by interfacial charge transfer in molecular assemblies on semiconductor substrates

“…In addition, the polarization response of molecular adsorbates to the image-charge field is expected to reduce the magnitude of the substrate screening. [62] The more delocalized nature of F 16 ZnPc's LUMO and ZnPc's molecular orbitals will result in a greater polarizability [64][65][66][67][68], as compared to the F 16 ZnPc's HOMO, leading to a larger reduction in the substrate screening. We speculate that the combination of these two effects is responsible for the experimental observation where the SOMO/HOMO-U of F 16 ZnPc is the only energetically varied orbital across the molecular overlayers.…”