Stability and physicochemical principles for icosahedral Ti(12)X(X = Li to Xe) clusters: A DFT study
ABSTRACT Results about stability, electronic structure and characteristic electronic properties are reported for cluster structures based on icosahedra structure with a composition of Ti12X (X = Li to Xe) within the generalized gradient approximation of the density functional theory. It is demonstrated that several elements allow an improvement on the stability of Ti13 by a doping process where the central atoms is substituted. C, Si, P, Co, Ge, Ru and Te lead to the largest gain in energy, while the HOMO-LUMO maximum gap distinguishes to just C, Si, P and Te as the most probable to be found in experimental samples. The analysis included physicochemical study of the most stable clusters to predict chemical affinity and new properties. Results reported here are in agreement with partial studies of Ti12X but because of the considered elements, a new scope is open of possible application mainly in the fields as sensors, catalysis and medicine, where the chemical selectivity is an important parameter.
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ABSTRACT: The present review surveys the results of X-ray diffraction studies of large stoichiometric transition metal clusters containing from 20 to 145 atoms in metal cores surrounded by ligand shells (72 compounds). Structures of such clusters have fragments of close packings (face-centered cubic (f.c.c.), hexagonal close (h.c.p.), and body-centered cubic (b.c.c.) packings) characteristic of crystalline bulk metals as well as mixed packings (f.c.c./h.c.p.), local close packings with pentagonal symmetry, and strongly distorted amorphous packings. The observed packing types, their distortions, and the relationship between the atomic structures of metal cores and the atomic radial distribution functions (RDF) are discussed. The structural principles established for the large clusters are applied to analysis of the experimental RDF for metal nanoparticles determined by X-ray diffraction and EXAFS spectroscopy.Russian Chemical Bulletin 01/2003; 52(11):2299-2327. DOI:10.1023/B:RUCB.0000012351.07223.d4 · 0.48 Impact Factor
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ABSTRACT: Over the last five decades, the isotope effect in solids has been one of the major researches in solid state science. Most of the physical properties of a solid depend to a greater or lesser degree on its isotopic composition. Scientific interest, technological promise and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor and insulator crystals. A great number of stable isotopes and well-developed methods of their separation have made it possible to date to grow crystals of C, LiH, ZnO, ZnSe, CuCl, GaN, GaAs, CdS, Cu2O, Si, Ge and α-Sn with a controllable isotopic composition. The use of such objects allows the investigation of not only the isotope effects in lattice dynamics (elastic, thermal and vibrational properties) but also the influence of such effects on the electronic states via electron–phonon coupling (the renormalization of the band-to-band transition energy Eg, the exciton binding energy Eb and the size of the longitudinal–transverse splitting ΔLT). Capture of thermal neutrons by isotope nuclei followed by nuclear decay produces new elements, resulting in a large number of possibilities for isotope selective doping of solids used in opto-, quantum electronics, fiber optics, etc. The nonlinear dependence of the free exciton luminescence (especially 12Cx13C1−x, LiHxD1−x) intensity on the excitation density allows us to consider these crystals as potential solid state lasers in the UV part of the spectrum. Isotopic information storage may consist in assigning the information “zero” or “one” to mono-isotopic microislands (or even to a single atom) within a bulk crystalline (or thin film) structure. Recent theoretical results confirm that quantum theory provides the possibility of new ways of performing efficient calculations. It shows how the use of quantum physics could revolutionize the way of communication and process information. Although modern computers rely on quantum mechanics to operate, the information itself is still encoded classically. A new approach is to treat information as a quantum concept and to ask what new insights can be gained by encoding this information in an individual quantum system. Isotope information storage and isotope quantum computers are briefly discussed. The review concludes with an outline of the main features of isotope physics in solids, and avenues for future research and applications.Progress in Materials Science 03/2006; 51(3):287-426. DOI:10.1016/j.pmatsci.2005.08.002 · 27.42 Impact Factor
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ABSTRACT: Density functional theory calculations using the generalized-gradient approximation have been carried out on the structural and electronic properties of Ti n and Ti n clusters for n3– 8 and 13. Many low-lying states, of different spins and geometries, were found for each Ti n and Ti n species. We observed that the calculated density of states DOS and the adiabatic electron binding energies for the ground state of a given anion are in good agreement with experimental photoelectron spectroscopy PES data, lending credence to the assignments of the ground state structures. Comparison between the calculated DOS and the PES data for other low-lying states made it possible to affirm contributions of these states to the spectra, allowing the characterization of the ensemble or composition of a given Ti n system. We found that all the clusters possess highly compact structures, and Ti 7 and Ti 13 have distorted pentagonal bipyramidal and icosahedral structures, respectively. From the ground state spin states, insight into the magnetic properties of the clusters and their evolution with size was also obtained. Small Ti clusters with n5 are highly magnetic, but the magnetic moment drops rapidly with size. © 2003 American Institute of Physics.The Journal of Chemical Physics 02/2003; 118(5). DOI:10.1063/1.1532000 · 2.95 Impact Factor