Fluxional and aromatic behavior in small magic silicon clusters: A full ab initio study of Sin, Sin1−, Sin2−, and Sin1+, n=6, 10 clusters

B11(-): a moving subnanoscale tank tread

We present a concept that an elongated, planar boron cluster can serve as a "tank tread" at the sub-nanometer scale, a novel propulsion system for potential nanomachines. Density functional calculations at the PBE0/6-311+G* level for the global-minimum B11(-)C2v ((1)A1) and B11C2v ((2)B2) structures along the soft in-plane rotational mode allow the identification of their corresponding B11(-)C2v and B11C2v transition states, with small rotational energy barriers of 0.42 and 0.55 kcal mol(-1), respectively. The energy barriers are refined to 0.35 and 0.60 kcal mol(-1) at the single-point CCSD(T) level, suggesting that the clusters are structurally fluxional at room temperature. Molecular dynamics simulations show that B11(-) and B11 behave exactly like a tank tread, in which the peripheral B9 ring rotates almost freely around the B2 core. A full turn of rotation may be accomplished in around 2 ps. In contrast to molecular wheels or Wankel motors, the peripheral boron atoms in the tank tread behave as a flexible chain gliding around, rather than as a rigid wheel rotation. This finding is beyond imagination, which expands the concepts of molecular wheels and Wankel motors.

Density functional studies of small silicon clusters adsorbed on graphene

The structural and electronic properties of small Si_n clusters (n = 1–6, 10) adsorbed on graphene are studied by use of density functional theory within periodic boundary conditions.

Vibrational spectra and structures of SinC clusters (n = 3–8)

The geometries of C-doped silicon clusters determined from infrared spectroscopy and computational chemistry reveal the stable Si₃C unit as a common structural motif.

Electronic, magnetic and optical properties of Cu, Ag, Au-doped Si clusters

The structural, optical and magnetic properties of Cu, Ag, Au-doped Si7 Clusters have been systematically investigated using density functional theory calculations. The global optimized structures of Cu, Ag, Au-doped Si clusters are predicted to have a lower HOMO-LUMO gap and higher magnetic moment. M-doping (M = Cu, Ag, Au) in Si cluster widens a range of adsorption wavelength, especially Au-doping. The characteristics in electronic density of states (DOSs) show that C5v-Si6Cu has a big asymmetrical spin-up and spin-down. The average atomic moment is 0.428 mμB per atom for the Si6Cu cluster with C5v symmetry, while the average paramagnetic moment is 0.143 mμB per atom for other M-doped (M = Cu, Ag, Au) Si7 clusters.

Theoretical study of the Si(5-n)(BH)n2- and Na(Si(5-n)(BH)n)- (n = 0-5) systems

The potential energy surfaces of the Na(Si(5-n)(BH)(n))(-) and Si(5-n)(BH)(n)(2-) (n = 0-5) systems have been explored in detail. We established that all the global minimum structures of anionic and dianionic systems can be obtained by substitution of one or more silicon atoms of the global minima of NaSi(5)(-) and Si(5)(2-) for B-H units. The conservation of the overall structure upon isoelectronic substitution was shown to be due to the preservation of the chemical bonding pattern. Theoretical VDEs were calculated for all of the sodiated Na(Si(5-n)(BH)(n))(-) (n = 0-5) systems to facilitate their experimental detection.

Structural identification of caged vanadium doped silicon clusters

The geometry of cationic silicon clusters doped with vanadium, Si(n)V(+) (n=12-16), is investigated by using infrared multiple photon dissociation of the corresponding rare gas complexes in combination with ab initio calculations. It is shown that the clusters are endohedral cages, and evidence is provided that Si(16)V(+) is a fluxional system with a symmetric Frank-Kasper geometry.

Designing novel Sn-Bi, Si-C and Ge-C nanostructures, using simple theoretical chemical similarities

A framework of simple, transparent and powerful concepts is presented which is based on isoelectronic (or isovalent) principles, analogies, regularities and similarities. These analogies could be considered as conceptual extensions of the periodical table of the elements, assuming that two atoms or molecules having the same number of valence electrons would be expected to have similar or homologous properties. In addition, such similar moieties should be able, in principle, to replace each other in more complex structures and nanocomposites. This is only partly true and only occurs under certain conditions which are investigated and reviewed here. When successful, these concepts are very powerful and transparent, leading to a large variety of nanomaterials based on Si and other group 14 elements, similar to well known and well studied analogous materials based on boron and carbon. Such nanomaterias designed in silico include, among many others, Si-C, Sn-Bi, Si-C and Ge-C clusters, rings, nanowheels, nanorodes, nanocages and multidecker sandwiches, as well as silicon planar rings and fullerenes similar to the analogous sp2 bonding carbon structures. It is shown that this pedagogically simple and transparent framework can lead to an endless variety of novel and functional nanomaterials with important potential applications in nanotechnology, nanomedicine and nanobiology. Some of the so called predicted structures have been already synthesized, not necessarily with the same rational and motivation. Finally, it is anticipated that such powerful and transparent rules and analogies, in addition to their predictive power, could also lead to far-reaching interpretations and a deeper understanding of already known results and information.

Heteroborane analogs of silicon clusters: experimental and theoretical studies on Bi2Si5 and Bi2Si5(-)

We have investigated the electronic structure of anionic and neutral Bi(2)Si(5) by means of anion photoelectron spectroscopy and density functional calculations. Both the experiments and calculations reveal that the Bi(2)Si(5)(-) anion prefers to adopt a distorted trigonal-bipyramidal structure with Bi(2) bridges. Following the isolobal analogy between divalent Si and B-H group, we show that both neutral Bi(2)Si(5) and neutral Bi(2)B(5)H(5) adopt similar pentagonal-bipyrmidal geometries and have analogous orbital energy patterns.

A new class of silicon-carbon clusters: a full study of the hydrogenated SinC2H2, n=3,4,5, clusters in comparison with their isoelectronic carboranes C2BnHn+2

The structural and electronic characteristics of the Si(n)C(2)H(2), n=3,4,5, clusters are studied by ab initio calculations based on coupled cluster and density functional theory using the hybrid B3LYP functional. It is demonstrated that all three clusters are structurally and electronically homologous to the corresponding isoelectronic organometallic carboranes C(2)B(n)H(n+2). This homology, which is in full agreement with the analogy of Si(6) (2-) and B(6)H(6) (2-) demonstrated recently by the author [J. Chem. Phys. 127, 014314 (2007)], includes not only the ground states but also the lower-lying isomers as well. These lowest lying isomers can be obtained by ortho, para, and meta substitutions from the corresponding Si(n) (2-), n=3,4,5, dianions. The energetic ordering of the low-lying isomers is in full agreement with the known valence and topological charge stability rules developed for carboranes. The hydrogenated clusters are much more stable than their nonhydrogenated counterparts. It is suggested that Si(3)C(2)H(2), Si(4)C(2)H(2), and Si(5)C(2)H(2), which can be probably found in interstellar space, are special examples of a general class of silicon-carbon clusters of the form Si(n)C(2)H(2), with analogous properties and similarities to the corresponding carboranes C(2)B(n)H(n+2). It is furthermore illustrated that the lowest energy structures of the Si(n)C(2) clusters can be obtained through a systematic and straightforward procedure from the Si(n)C(2)H(2) clusters. The present results could hopefully make possible the exploitation of the rich borane and carborane chemistry for the design and development of novel silicon and silicon-carbon composite nanomaterials.