Structural and electronic properties of small beryllium clusters: a theoretical study

Geometric structures and electronic properties of small beryllium clusters (Be(n), 2< or = n< or =9) are investigated within the gradient-corrected density functional theory. The computations are performed with the Becke exchange and Perdew-Wang correlation functionals. Both low and high multiplicity states are considered. A predominance of higher multiplicity states among the low-energy isomers of the larger clusters is found. An analysis of the variations in the structural and electronic properties with cluster size is presented, and the results are compared with those of earlier studies.     

Inorganic electride: theoretical study on structural and electronic properties

We report self-consistent ab initio calculations of structural and electronic properties for a kind of recently synthesized inorganic electride. The optimized geometry gives zigzag cesium chains within the sinusoidal channels of the zeolite. Among the wide energy gap of the zeolite, near the conduction bands, there are two interstitial electride bands mainly contributed by 6s electrons of Cs atoms, which have a delocalized real space distribution along the channels. For all different doping rates studied, we find that a finite density of states appears at the Fermi level, which predicts a metallic behavior of this material. Detailed electronic structure reveals all the essential properties of the electride model. The shift of Fermi level and the delocalization of the highest occupied bands cause this material to be a powerful reducing agent.     

Density functional study of structural and electronic properties of small bimetallic silver-nickel clusters

Theoretical study on the structure and electronic properties of small AgmNip (m + p < or = 6) clusters has been carried out in the framework of density functional theory. Structural features, cohesive energies, vertical ionization potentials, and charge transfers are evaluated for each Ag/Ni ratio. In all the AgmNip clusters, the nickel atoms are brought together, yielding a maximum of Ni-Ni bonds, and the silver atoms are located around a Ni core with a maximum of Ag-Ni bonds. The ionization potential and the highest occupied molecular orbital shape are directly related to the two- or three-dimensional character of the cluster's geometry. A very low electronic charge transfer from Ni to Ag is found, and the magnetic moment is located on Ni atoms but with a low spin polarization on silver in the Ni-rich clusters.     

Probing the structural and electronic properties of small vanadium monoxide clusters

The structural evolution and bonding of a series of early transition-metal oxide clusters, V(n)O(q) (n = 3-9, q = 0,-1), have been investigated with the aid of previous photoelectron spectroscopy (PES) and theoretical calculations. For each vanadium monoxide cluster, many low-lying isomers are generated using the Saunders "Kick" global minimum stochastic search method. Theoretical electron detachment energies (both vertical and adiabatic) were compared with the experimental measurements to verify the ground states of the vanadium monoxide clusters obtained from the DFT calculations. The results demonstrate that the combination of photoelectron spectroscopy experiments and DFT calculation is not only powerful for obtaining the electronic and atomic structures of size-selected clusters, but also valuable in resolving structurally and energetically close isomers. The second difference energies and adsorption energies as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. The adsorption energies of one O atom on the anionic (6.64 → 8.16 eV) and neutral (6.41 → 8.13 eV) host vanadium clusters are shown to be surprisingly high, suggesting strong capabilities to activate O by structural defects in vanadium oxides.     

Ab initio study on structural and electronic properties of BanOm clusters

Density-functional calculation within local density approximation, shows that the electronic property of a barium oxide cluster is strongly correlated with its equilibrium structure. The ground-state structures of BanOm (4 < or = n < or = 9,m < or = n) clusters can be classified into four categories: (a) compact, (b) dangling state, (c) F-center, and (d) stoichiometric. The compact cluster is metallic, almost no energy gap exists between the highest occupied and the lowest unoccupied molecular orbitals. The energy gap for the dangling state cluster is larger than that for the F-center cluster, while the stoichiometric cluster has the largest energy gap.     

A theoretical study on Ta(n)+ cluster cations: structural assignments, stability, and electronic properties

The low-lying structures of tantalum cluster cations up to n = 16 are investigated using hybrid HF/density functional theory (DFT) functionals (B3P86) in conjunction with relativistic effective core potential and corresponding basis set. The vibrational spectra of tantalum cluster cations are simulated with one empirical scaling factor of 0.943, and compared to the experimental ones [P. Gruene, A. Fielicke, G. Meijer, J. Chem. Phys. 127, 234307 (2007)]. By assigning the vibrational peaks of experimental spectra, the favored geometries actually existing in the molecular beam are obtained for several studied clusters. Based on the favored geometries, the relative stabilities, spin magnetic moments, and electronic dipole moments are determined. Furthermore, spin-related indices (ω(s) (±)) are computed and found to be good linear correlation with vertical lower-upper energy gap.     

Structural,electronic and magnetic properties of small gold clusters with a copper impurity

A set of all-electron scalar relativistic calculations on Au _n Cu (n = 1–12) clusters has been performed using density functional theory with the generalized gradient approximation at PW91 level. The lowest energy geometries of Au _n Cu clusters may be considered as assemblies of triangular Au₃ moieties substituted with one Cu atom at the highest coordinated site. All these lowest energy geometries of the Au _n Cu clusters are slightly distorted but retain the planar structures of the Au _n+1 clusters due to the strong scalar relativistic effects. The Au–Cu bonds are stronger, and a few Au–Au bonds far from the Cu atom are weaker, than the corresponding Au–Au bonds in pure Au _n+1 clusters. After doping with a Cu atom, the thermodynamic stability and chemical reactivity are enhanced to some extent. The odd-numbered Au _n Cu clusters with even numbers of valence electrons are more stable than the neighboring even-numbered Au _n Cu clusters with odd numbers of valence electrons. Odd–even alternations of magnetic moments and electronic configurations for the Au _n Cu clusters can be observed clearly and may be understood in terms of the electron pairing effect.     

Size-dependent structural evolution and chemical reactivity of gold clusters.

Ground-state structures and other experimentally relevant isomers of Au(15) (-) to Au(24) (-) clusters are determined through joint first-principles density functional theory and photoelectron spectroscopy measurements. Subsequent calculations of molecular O(2) adsorption to the optimal cluster structures reveal a size-dependent reactivity pattern that agrees well with earlier experiments. A detailed analysis of the underlying electronic structure shows that the chemical reactivity of the gold cluster anions can be elucidated in terms of a partial-jellium picture, where delocalized electrons occupying electronic shells move over the ionic skeleton, whose geometric structure is strongly influenced by the directional bonding associated with the highly localized "d-band" electrons.     

A theoretical study of the structural and electronic properties of some titanocenes using DFT,TD-DFT,and QTAIM

Structural Chemistry - Titanocenes are gradually proven to possess good anticancer activity. In this paper, we present a theoretical study of some properties of six promising anticancer titanocenes...     

Ground state, growth, and electronic properties of small lanthanum clusters

The DMol cluster method based on density-functional theory has been employed to study the structural stability and electronic structure of La(n) (n=2-14) clusters. The ground states have been found out for lanthanum clusters. The Jahn-Teller effect plays an important role in this process because there are many isomers near the ground state. The magnetism is not sensitive to interatomic spacing when the change of interatomic spacing is in a small range. Lanthanum clusters grow in an icosahedral pattern. The results of the mean binding energy, of the second derivative of binding energy, and of the formation energy show strong odd-even alternation and that 7- and 13-atom clusters are magic. Further, the HOMO-LUMO gap, the mean nearest bond lengths, and the mean magnetic moments suggest that the convergence to bulk is slow and it shows an oscillatory behavior for small lanthanum clusters.     

Structural, electronic, and magnetic properties of manganese-doped Zn12O12 clusters: a first-principles study

A first-principles study has been performed to evaluate the structural, electronic, and magnetic properties of Zn(12)O(12) clusters doped with one or two Mn atoms. The substitutional, exohedral, and endohedral dopings are taken into account. For the monodoped clusters, the substitutional isomer is most energetically favorable, and an exohedral isomer may appear as a low-lying metastable state. All isomers present 5 mu(B) magnetic moment that is mainly contributed by the Mn-3d component. For the bidoped clusters, the antiferromagnetic state is degenerate with the ferromagnetic state at larger Mn-Mn distance (>5 A), while it is more energetically favorable at smaller Mn-Mn distance. Thus, the cohesion of bidoped isomer is sensitive to the magnetic coupling or chemical bonding. The endohedral bidoped isomer is found to be a stable local minimum, and the direct Mn-Mn interaction causes the reduction of local magnetic moment of Mn to about 4 mu(B).     

Complexes of small neutral gold clusters and hydrogen sulphide: A theoretical study

Binding energies, geometries, charge transfers and vibrational frequencies of complexes of neutral gold clusters Au_n (n = 1–4) and H₂S are computed using density functional theory. The geometries of Au_n and H₂S are little changed upon complex formation but, for the Au₄SH₂ complex, one of the two low-lying Au₄ isomers is more stabilized by H₂S due to intracomplex hydrogen bonding and may be the lowest-energy Au₄SH₂ structure. For the complexes, computed infrared and Raman spectra are discussed with a focus on distinguishing between the two candidates for the lowest-energy Au₄SH₂ structure.     

High-nuclearity iridium carbonyl clusters containing phenylgermyl ligands: synthesis, structures, and reactivity

The reaction of Ir4(CO)12 with Ph3GeH at 97 degrees C has yielded the new tetrairidium cluster complexes Ir4(CO)7(GePh3)(mu-GePh2)2[mu3-eta3-GePh(C6H4)](mu-H)2 (10) and Ir4(CO)8(GePh3)2(mu-GePh2)4 (11). The structure of 10 consists of a tetrahedral Ir4 cluster with seven terminal CO groups, two bridging GePh2) ligands, an ortho-metallated bridging mu3-eta3-GePh(C6H4) group, a terminal GePh3 ligand, and two bridging hydrido ligands. Compound 11 consists of a planar butterfly arrangement of four iridium atoms with four bridging GePh2 and two terminal GePh3 ligands. The same reaction at 125 degrees C yielded the two new triiridium clusters Ir3(CO)5(GePh3)(mu-GePh2)3(mu3-GePh)(mu-H) (12) and Ir3(CO)6(GePh3)3(mu-GePh2)3 (13). Compound 12 contains a triangular Ir3 cluster with three bridging GePh2), one triply bridging GePh, and one terminal GePh3 ligand. The compound also contains a hydrido ligand that bridges one of the Ir-Ge bonds. Compound 13 contains a triangular Ir3 cluster with three bridging GePh2 and three terminal GePh3 ligands. At 151 degrees C, an additional complex, Ir4H4(CO)4(mu-GePh2)4(mu4-GePh)2 (14), was isolated. Compound 14 consists of an Ir4 square with four bridging GePh2, two quadruply bridging GePh groups, and four terminal hydrido ligands. Compound 12 reacts with CO at 125 degrees C to give the compound Ir3(CO)6(mu-GePh2)3(mu3-GePh) (15). Compound 15 is formed via the loss of the hydrido ligand and the terminal GePh3 ligand and the addition of one carbonyl ligand to 12. All compounds were fully characterized by IR, NMR, single-crystal X-ray diffraction analysis, and elemental analysis.     

Geometries, stabilities, and electronic properties of small anion Mg-doped gold clusters: a density functional theory study

First-principle density functional theory is used for studying the anion gold clusters doped with magnesium atom. By performing geometry optimizations, the equilibrium geometries, relative stabilities, and electronic and magnetic properties of [Au(n)Mg]? (n = 1-8) clusters have been investigated systematically in comparison with pure gold clusters. The results show that doping with a single Mg atom dramatically affects the geometries of the ground-state Au(n+1)? clusters for n = 2-7. Here, the relative stabilities are investigated in terms of the calculated fragmentation energies, second-order difference of energies, and highest occupied?lowest unoccupied molecular orbital energy gaps, manifesting that the ground-state [Au(n)Mg]? and Au(n+1)? clusters with odd-number gold atoms have a higher relative stability. In particular, it should be noted that the [Au?Mg]? cluster has the most enhanced chemical stability. The natural population analysis reveals that the charges in [Au(n)Mg]? (n = 2-8) clusters transfer from the Mg atom to the Au frames. In addition, the total magnetic moments of [Au(n)Mg]? clusters exhibit an odd-even oscillation as a function of cluster size, and the magnetic effects mainly come from the Au atoms.     

Structure of small TiCn clusters: A theoretical study

A theoretical study of the TiC_n (n = 1–8) clusters has been carried out at the B3LYP/6-311+G(d) level. Molecular properties for three different isomers, namely linear, cyclic, and fan species, have been determined. The fan isomers, where the titanium atom is essentially side-bonded to the entire C_n unit, are predicted to be more stable than both linear and cyclic isomers. Only for the largest studied species, TiC₈, the cyclic isomer is located lower in energy. An even–odd parity effect in the incremental binding energies is observed for the three isomers, n-even species being in general more stable for linear and fan isomers, whereas for the cyclic species n-odd clusters are favoured. A topological analysis of the electronic charge density shows that all cyclic isomers correspond to true monocyclic rings, whereas for the fan species a variety of different connectivities has been observed.     

A density-functional study of the structural, electronic, magnetic, and vibrational properties of Ti8C12 metallocarbohedrynes

Calculations are presented for the structural, electronic, and vibrational properties of the different Ti8C12 metallocarbohedrynes. (Please note that we adopt the name "metallocarbohedrynes" instead of "metallocarbohedrenes" to denote the acetylenic nature of C2 units in this class of clusters demonstrated by several contributions in literature.) The density-functional theory (DFT) calculations are performed with the all-electron projector augmented-wave method and generalized gradient approximation for the exchange-correlation functional. We study the seven low-energy isomers of the Ti8C12 metallocarbohedrynes using spin-polarized DFT, where we find a correlation between the number of rotated carbon dimers and the cohesive energy of the structure. The electronic density of states (eDOS) show that C3nu, D*3d, and D3d isomers are spin polarized. The partial eDOS shows that, depending on the dimer orientation, carbon atoms and a subgroup of the metal atoms form a covalent framework while other metal atoms are bonded to this framework more ionically. This picture is further supported by the charge density of the different structures, where we see that the Ti atoms with higher charge density show less contribution to the covalent bonding of the Ti-C framework. The vibrational spectra of the different structures are calculated using the frozen-vibration method. Also, we calculate the vibrational spectra of the C3nu and C2nu structures using molecular-dynamics simulations at two different temperatures. The results of the simulations demonstrate the local stability of the structures beyond the harmonic limit explored by the frozen-vibration method.     

Generation, structure and reactivity of arynes: A theoretical study

The semiempirical AM1 SCF-MO method is used to study the benzyne mechanism for aromatic nucleophilic substitution of various m-substituted chlorobenzenes and 3-chloropyridine. The calculations predict that most of the fixed substituents studied here would induce the formation of 2,3-arynes through their electron-withdrawing resonance or inductive effects. The geometry and electronic structure of the 2,3- and 3,4-arynes investigated here, confirm the generally acceptedo-benzyne structure postulated for arynes. The sites of nucleophilic addition to arynes as predicted here are in fair agreement with expectation and experimental findings.     

A theoretical study about the structural, electronic and spectroscopic properties of the ground and singlet excited states of curcuminoidic core

Curcumin, a well-known Indian spice, holds a variety of properties in many different fields from medicinal chemistry to dye industry. The peculiar electronic structure makes curcumin a valuable metal chelator. The principal aim of this work is a computational study of the structural and electronic properties of the ground and the first singlet excited states of the curcuminoidic core. Concerning the ground state, tautomeric equilibrium, vibrational and thermochemical analysis and electronic absorption spectra (with ab initio and semi-empirical methodologies) have been studied. A full geometry optimization of the first singlet excited states was obtained, with different computational methodologies. Solvent effects are also implicitly considered. An accurate comparison of the results is presented. Interesting aspects emerge, which suggest successive investigation about the nature of the excited states. The obtained results may be of large applicative interest. If curcuminoids are considered as potential ligands for complexes formation with metallic ions of pharmaceutical, medical–physical and technological interest, exciting the system with photons of appropriate frequencies, a photomodulated release of the metallic ion in the environment might be guessed, because of an important photoinduced geometrical modification.     

Geometries,stabilities, electronic and magnetic properties of small aluminum cluster anions doped with cobalt: A density functional theory study

The geometrical structures, relative electronic and magnetic properties of small Al_nCo^– (1 ≤ n ≤ 9) clusters are systematically investigated within the framework of density functional theory at the BPW91 level. The single Co doping can dramatically affect the ground state geometries of the 1 Al_n+1^- clusters. At the same time, the resulting geometries show that the lowest energy Al_nCo^– clusters prefer to be three dimensional structures. Here, the relative stabilities are investigated in terms of the calculated average binding energies, fragmentation energies, and second-order energy differences. Moreover, the result of the highest occupiedlowest unoccupied molecular orbital energy gaps indicates that Al₆Co^– clusters have the highest chemical stability for Al_nCo^– (1 ≤ n ≤ 9) clusters. Furthermore, the natural population analysis reveals that the charges in Al_nCo^– clusters transfer from the Al frames to the Co atom. Additionally, the analyses of the local and total magnetic moments of the Al_nCo^– clusters show that the magnetic effect mainly comes from the Co atom.     

Synthesis, reactivity, and electronic structure of [n]vanadoarenophanes: an experimental and theoretical study

An optimized procedure for the selective dimetalation of [V(eta (6)-C 6H 6) 2] by BuLi/tmeda allowed for the isolation and characterization of [V(eta (6)-C 6H 5Li) 2].tmeda. X-ray diffraction of its thf solvate [V(eta (6)-C 6H 5Li) 2].(thf) 7 revealed an unsymmetrical, dimeric composition in the solid state, in which both subunits are connected by three bridging lithium atoms. Treatment with several element dihalides facilitated the isolation of [ n]vanadoarenophanes ( n = 1, 2) with boron and silicon in the bridging positions. In agreement with the number and covalent radii of the bridging elements, these derivatives exhibit molecular ring strain to a greater or lesser extent. The B-B bond of the [2]bora species [V(eta (6)-C 6H 5) 2B 2(NMe 2) 2] was readily cleaved by [Pt(PEt 3) 3] to afford the corresponding oxidative addition product. Subsequently, [V(eta (6)-C 6H 5) 2B 2(NMe 2) 2] was employed as a diborane(4) precursor in the diboration of 2-butyne under stoichiometric, homogeneous, and heterogeneous catalysis conditions. This transformation is facilitated by the reduction of molecular ring strain, which was confirmed by a decrease of the tilt angle alpha observed in the corresponding solid-state structures. EPR spectroscopy was used to probe the electronic structure of strained [ n]vanadoarenophanes and revealed an obvious correlation between the degree of molecular distortion and the observed hyperfine coupling constant a iso. State-of-the-art DFT calculations were able to reproduce the measured isotropic vanadium hyperfine couplings and the coupling anisotropies. The calculations confirmed the decrease of the absolute isotropic hyperfine couplings with increasing tilt angle. Closer analysis showed that this is mainly due to increased positive contributions to the spin density at the vanadium nucleus from the spin polarization of doubly occupied valence orbitals of vanadium-ligand sigma-antibonding character. The latter are destabilized and thus made more polarizable in the bent structures.