Geometric structure and electron spectrum of YSi n − clusters (n = 6–17)

Results of the optimization of the geometric structure of YSi _n ^? anion clusters (n = 6–17) have been presented and their electron spectra have been calculated. Calculations have been performed by the density functional theory method. Actual geometric structures of clusters have been established by comparing the calculated and known experimental data.     

Spatial and electronic structures of the germanium-tantalum clusters TaGe n − (n = 8–17)

The results of optimizing the spatial structure and calculated electronic spectra of the TaGe _n ^? anion clusters (n = 8–17) have been presented. The calculations have been performed in terms of the density functional theory. The most probable spatial structures of clusters detected in the experiment have been determined by comparing the calculated and available experimental data.     

Structures and energetics of BenGen (n = 1–5) and Be2nGen (n = 1–4) clusters

Cluster geometries and energies of Be_nGe_n (n = 1–5) and Be_2nGe_n (n = 1–4) have been examined in theoretical electronic structure calculations. Structure optimisations were carried out using DFT B3LYP/6-31G(2df) and the energies of the optimum geometries were ordered in QCISD(T) calculations. Be and Ge bond to each other and to other atoms of their own kind, creating a great variety of low-energy clusters in a variety of structural types. Comparisons of the germanide clusters with previously explored silicide and carbide structures reveal some structural similarities, but the germanides have much more in common with the beryllium silicides than with the carbides. However, germanide clusters show a greater tendency to form cage-like structures with potential in technological applications.     

First-principles calculations of the structural, electronic and magnetic properties of BnN20−n (n = 6−18) clusters

The structures of B _n N_20 ? n    (n = 6?18), the clusters of boron nitride, are investigated by the density functional theory calculations. The structures of the obtained low-lying isomers can be described by the following six prototypes: single ring, double ring, three-ring, graphitic-like sheet, fullerene and others. B₁₀N₁₀ is demonstrated to be the most stable cluster against the nonstoichiometric ones. Nonzero magnetic moments, 1.999, 1.998, 2.000, 3.999 and 1.999μ _B respectively, are found in five B _n N_20?n (n = 6, 7, 11, 12, 13) clusters. Further analysis indicates that the magnetic moment of the B₆N₁₄ cluster is mainly originated from the N atoms, while those of others are from the B atoms. The magnetic moment are finally attributed to the interesting issues of the 2p electrons due to the breaking of local symmetries, the change of coordination number, charge distribution and orbital hybridization.     

The PF6−n(R)n− anions (R = CH3, C2H5; n = 0–6): the dependence of the electronic stability on the number of non-electronegative alkyl ligands

The PF_6?n(R)_n^? superhalogen anions (where R = CH₃, C₂H₅ and n = 1–6) were investigated at the ab initio OVGF/6-311++G(3df,3pd)//MP2/6-311++G(d,p) level of theory and their electronic and thermodynamic stabilities were compared to those of the reference PF₆^? system. It is demonstrated that (1) the presence of six substituents bound to the phosphorus atom is an important factor that enables the stability of the PF_6?n(R)_n^? anions; (2) subsequent replacement of the fluorine ligands with alkyl R groups in the PF₆^? superhalogen anion results in a substantial electronic stability decrease (by 2.38–6.74 eV); (3) when the certain number of alkyl substituents is achieved, the PF_6?n(R)_n^? anions become thermodynamically unstable.     

Lattice dynamics and electronic structure of cobalt–titanium spinel Co2TiO4

Physics of the Solid State - The results are presented on phonon excitations and the electronic structure of Co2TiO4 inverse spinel in which magnetically ordered cobalt ions Co2+ (3d 7) are in...     

The molecular and electronic structure of N,N′-ethylenebis(acetylacetonylideiminato)oxovanadium(IV) and the electronic structure of its thio analogue

The electronic structures of the title complexes—VO(acen) and VS(acen)—and the free H₂(acen) ligand are probed using gas-phase UV-photoelectron spectroscopy [acen = N,N′-ethylenebis(acetylacetonylideiminato)]. The effect of the different axial donors on the metal center is examined, as is the effect that the oxo and thio ligands have on the acen orbitals. We find that the oxo and thio donors primarily affect the metal center and that the ligand periphery remains mostly unchanged.     

Structural evolutions and electronic properties of Au_nGd(n=6–15) small clusters: A first principles study

Structural, electronic, and magnetic properties of Au_nGd(n = 6–15) small clusters are investigated by using first principles spin polarized calculations and combining with the ab-initio evolutionary structure simulations. The calculated binding energies indicate that after doping a Gd atom Aun Gd cluster is obviously more stable than a pure Au_(n+1) cluster.Au_6Gd with the quasiplanar structure has a largest magnetic moment of 7.421 μ_B. The Gd-4 f electrons play an important role in determining the high magnetic moments of Au_nGd clusters, but in Au_6Gd and Au_(12) Gd clusters the unignorable spin polarized effects from the Au-6 s and Au-5 d electrons further enhance their magnetism. The HOMO–LUMO(here, HOMO and LUMO stand for the highest occupied molecular orbital, and the lowest unoccupied molecular orbital, respectively)energy gaps of Au_nGd clusters are smaller than those of pure Au_(n+1) clusters, indicating that Au_nGd clusters have potential as new catalysts with enhanced reactivity.     

Geometries,stabilities and electronic properties of small-sized Pd2-doped Sin (n = 1–11) clusters

The geometries, growth patterns, relative stabilities and electronic properties of small-sized Pd₂Si_n and Si_n+2 (n = 1–11) clusters are systematically studied using the hybrid density functional theory method B3LYP. The optimised structures revealed that the lowest energy Pd₂Si_n clusters are not similar to those of pure Si_n clusters. When n = 9, one Pd atom in Pd₂Si₉ completely falls into the centre of the Si outer frame, forming metal-encapsulated Si cages. On the basis of the optimised structures, the averaged binding energy, fragmentation energy, second-order energy difference and highest occupied–lowest unoccupied molecular orbital energy gap are calculated. It is found that the Pd₂Si₅ and Pd₂Si₇ clusters have stronger relative stabilities among the Pd₂Si_n clusters. Additionally, the stabilities of Si_n+2 clusters have been reduced by the doping of Pd impurity. The natural population and natural electronic configuration analysis indicated that the Pd atoms possess negative charges for n = 1–11 and there exist the spd hybridisation in the Pd atom. Finally, the chemical hardness, chemical potential, electrostatic potential and polarisability are discussed.     

Specific features of the electronic structure and spectral properties of NdNi5 − x Cu x compounds

The spectral properties of the intermetallic compounds NdNi_{5 ? x} Cu _x (x = 0, 1, 2) have been studied using optical ellipsometry in the wavelength range 0.22–16 μm. It has been established that substitution of copper atoms for nickel leads to noticeable changes in the optical absorption spectra, plasma frequencies, and relaxation frequencies of conduction electrons. Spin-polarized calculations of the electronic structure of these compounds have been performed in the local spin density approximation allowing for strong electron correlations (LSDA + U method) in the 4f shell of the rare-earth ion. The calculated electron densities of states have been used to interpret the experimental dispersion curves of optical conductivity in the interband light absorption region.     

Probing the structural and electronic properties of cationic rubidium–gold clusters: [AunRb]+ (n = 1–10)

Density functional theory has been applied to study the geometric structures, relative stabilities, and electronic properties of cationic [Au_nRb]⁺ and Au_{n + 1}⁺ (n = 1–10) clusters. For the lowest energy structures of [Au_nRb]⁺ clusters, the planar to three-dimensional transformation is found to occur at cluster size n = 4 and the Rb atoms prefer being located at the most highly coordinated position. The trends of the averaged atomic binding energies, fragmentation energies, second-order difference of energies, and energy gaps show pronounced even–odd alternations. It indicated that the clusters containing odd number of atoms maintain greater stability than the clusters in the vicinity. In particular, the [Au₆Rb]⁺ clusters are the most stable isomer for [Au_nRb]⁺ clusters in the region of n = 1–10. The charges in [Au_nRb]⁺ clusters transfer from the Rb atoms to Au_n host. Density of states revealed that the Au-5d, Au-5p, and Rb-4p orbitals hardly participated in bonding. In addition, it is found that the most favourable channel of the [Au_nRb]⁺ clusters is Rb⁺ cation ejection. The electronic localisation function (ELF) analysis of the [Au_nRb]⁺ clusters shown that strong interactions are not revealed in this study.     

The theoretical and experimental investigations of Stark structure in sodium Rydberg states atoms

The experimental results of the Stark structure of Na in the vicinity of n~*=21-23 with the external electric field from 0 to 380V/cm are reported. The theoretical calculation of the stark levels of Na based on the atomic potential model are in good agreement with experiment. The limiting error between the theory and experiment turns out to be due to experimental uncertainty.     

First principles calculations of the structural and electronic properties of(CdSe)n clusters

The structural and electronic properties of (CdSe)n(1≤n≤5) clusters are calculated using density functional theory within the pseudopotential and generalized gradient approximations. The calculated binding energies and highest occupied molecular orbital lowest unoccupied molecular orbital gaps are compared with those obtained within local density approximation.     

Hyperfine structure and isotope shift investigations in202–222Rn for the study of nuclear structure beyond Z=82

The hyperfine structure (hfs) and isotope shift (IS) in the isotopic chain of the radioactive element radon have been studied for the first time. The measurements were carried out by collinear fast-beam laser spectroscopy at the mass separator facility ISOLDE at CERN. The IS between 16 isotopes in the mass range 202A222 and the hfs of 7 odd-A isotopes were determined in the transitions 7s [3/2]₂-7p [5/2]₃ (745 nm) of Rn I. The nuclear spins and moments, as well as the observed inversion of the odd-even staggering for^218–222Rn, can be associated with the effects of octupole instability around N=134.This work was supported by the Bundesministerium für Forschung und Technologie and the Deutsche Forschungsgemeinschaft.     

Resonance Raman excitation and electronic structure of the single bonded dimers (C ¯60)2 and (C 59N)2

Raman spectra are presented for the single bonded dimeric fullerene (C ₆₀ ^- ) ₂ and compared to optical spectra and Raman spectra of the isostructural and isoelectronic heterofullerene (C₅₉N)₂. The spectra of both materials exhibit strong correlations with respect to splitting, line position, and line intensity. This holds for non resonant excitation with blue and green lasers as well as for the strong resonances observed with red lasers. The latter observation is consistent with a downshift for the electronic transition energies as compared to C₆₀. The absorption edge of thin films of (C₅₉N)₂ was found at 1.4 eV. The three intercage modes were observed at 82, 103, and 111, and at 88, 98, and 106 cm^-1 for (C₅₉N)₂ and (C ₆₀ ^- ) ₂ , respectively. A surprising difference was found for the position of the pentagonal pinch modes in the two materials as they were observed at 1461 and at 1451 cm^-1, for (C₅₉N)₂ and (C ₆₀ ^- ) ₂ , respectively. This is interpreted as a consequence of some characteristic differences in the electronic structure of the two compounds. Received 25 January 2000 and Received in final form 10 April 2000     

Characterisation of the Fermi surface and phase transitions of (BEDO-TTF)2 ReO4·(H2O) by physical property measurements and electronic band structure calculations

The electronic properties of the organic superconductor (BEDO-TTF)₂ ReO₄·(H₂O) were investigated by temperature dependent resistivity, ESR, Hall effect and magnetoresistance measurements. Shubnikov-de Haas (SdH) oscillations were observed in magnetic fields up to 24 T in the temperature range 0.5 K to 4.2 K. The electronic band structure of (BEDO-TTF)₂ ReO₄·(H₂O) was calculated by employing the extended Hückel tight binding method on the basis of its room temperature crystal structure. The two observed SdH frequencies of 75 T and 37 T correspond very well with two cross-sectional areas of the hole and electron Fermi surface pockets obtained from the tight binding calculation. From the temperature dependence of the SdH oscillation amplitudes, the cyclotron effective mass (m_c) belonging to the larger and smaller pockets were found to be 0.9 m₀ and m_c=1.15 m₀ respectively. Measurements of the angular dependence of the SdH frequencies show no deviation from that expected for a cylindrical Fermi surface. In terms of our tight binding calculations and experimental measurements, probable causes for the 213 K and 35 K phase transitions are discussed. The calculations show that (BEDO-TTF)₂ ReO₄·(H₂O) is a two dimensional semimetal but possesses a hidden nesting. The latter is likely to cause an SDW instability leading to the 35 K transition. The resistivity drop associated with the 213 K transition is likely to be induced by an abrupt increase in the relaxation time. The excellent agreement between the calculated and experimentally observed Fermi surface implies that, with decreasing temperature below 35 K, (BEDO-TTF)₂ ReO₄·(H₂O) gradually gets out of the SDW state and re-enters the original metallic state, in which it becomes superconducting below 2.4 K.Reported at the 13th Genral Conference of the Condensed Matter Division of the European Physical Society, Regensburg, March 1993     

Bottom-up substitution assembly of AuF4−n0,−+nPO3 (n = 1–4): a theoretical study of novel oxyfluoride hyperhalogen molecules and anions AuF4−n(PO3)n0,−

Compounds with high electron affinity, i.e. superhalogens, have continued to attract chemists’ attention, due to their potential importance in fundamental chemistry and materials science. It has now proven very effective to build up novel superhalogens with multi-positively charged centres, which are usually called ‘hyperhalogens’. Herein, using AuF₄^? and PO₃ as the model building blocks, we made the first attempt to design the Au,P-based hyperhalogen anions AuF_4?n(PO₃)_n^? (n = 1–4) at the B3LYP/6-311+G(d)&;SDD and CCSD(T)/6-311+G(d)&;SDD (single-point) levels (6-311+G(d) for O, F, P and SDD for Au). Notably, for all the considered Au,P systems, the ground state bears a dioxo-bonded structure with n ≤ 3, which is significantly more stable than the usually presumed mono-oxo-bonded one. Moreover, the clustering of the –PO₃ moieties becomes energetically favoured for n ≥ 3. The ground states of AuP₄O₁₂^0,? are the first reported cage-like oxide hyperhalogens. Thus, the ?PO₃ moiety cannot be retained during the ‘bottom-up’ assembly. The vertical detachment energy (VDE) value of the most stable AuF_4?n(PO₃)_n^? (n = 1–4) ranges from 7.16 to 8.20 eV, higher than the VDE values of the corresponding building blocks AuF₄^? (7.08 eV) and PO₃^? (4.69 eV). The adiabatic detachment energy values of these four hyperhalogens exceed 6.00 eV. Possible generation routes for AuF_4?n(PO₃)_n^? (n = 1–4) were discussed. The presently designed oxyfluorides not only enriches the family of hyperhalogens, but also demonstrates the great importance of considering the structural transformation during the superhalogen → hyperhalogen design such as for the present Au–P based systems.