Large HOMO-LUMO Gap Research Articles

Density functional theory study of hydrogen adsorption on C@Al12 cluster

Density functional theory has been employed to investigate the structure and stability of C@Al12Hn (1≤n≤7) clusters. Hydrogenated C@Al12 clusters exhibit pronounced stability for even numbers of H atoms. Large HOMO-LUMO gaps，large binding energy and increased ionization potentials imply that these clusters should be physically and chemically stable. The analysis of the charge density of the HOMO plot illustrates that a pair of hydrogen atoms prefer to occupy opposing on-top sites for clusters with an even n number. Studies of deformation charge density plots demonstrate that the bonding characteristic between the H atoms and the C@Al12 moiety is mainly covalent. The total magnetic moment is 1μB for C@Al12Hn with an odd number for n.

Trends in the formation of aggregates and crystals from M@Si16 clusters: a study from first principle calculations

We have shown recently that the ground state and low-lying energy isomers of the endohedral M@Si16 clusters (M = Sc−, Ti, V+) have a nearly spherical cage-like symmetry with a closed shell electronic structure which conforms them as exceptional stable entities. This is manifested, among other properties, by a large Homo–Lumo gap about 2 eV which suggest the possibility of using these clusters as basic units (superatoms) to construct optoelectronic materials. As a first step in that direction, we have studied in this work, by means of first principles calculations, the trends in the formation of [Ti@Si16]n, [Sc@Si16K]n, and [V@Si16F]n aggregates as their size increases, going from linear to planar to three dimensional arrangements. The most favorable configurations for n ≥ 2 are those formed from the fullerene-like D4d isomer of M@Si16, instead of the ground state Frank–Kasper Td structure of the isolated M@Si16 unit, joined by Si–Si bonds between the Si atoms of the square faces. In all cases the Homo–Lumo gap for the most favorable structure decrease with the size n. Trends for the binding energy, dipole moment, and other electronic properties are also discussed. Several crystal structures constructed from these superatom, supermolecules, and aggregates have been tested and preliminary results are summarily commented.

Are In 13M (M = Li, Na, K) magic clusters? – A comparison with Al 13M

Density functional study was performed on the stability of In n M ( n = 11–15, M = Li, Na, K) clusters. In 13M are characterized by electronic shell closure with enhanced stability, larger HOMO–LUMO gap, higher ionization potential, and lower electron affinity as compared with clusters of adjacent sizes, while very similar size dependence was found between In n M and Al n M in their electronic properties, suggesting that In 13M be magic clusters and promising as building blocks in developing cluster-assembled materials. The calculated AEA of In 13 is close to that of iodine, implying it would behave like a halogen atom in ionic In 13M molecule.

Theoretical study on a family of organic molecules with planar tetracoordinate carbon

Based on the most stable structure of C 3B 2H 4 and its substitution of H with -Cl, -CH 2OH, -CHOH, -C O and -COOH groups, a series of derivatives containing the planar tetracoordinate carbon (ptC) atoms as well as crown ether-like compounds from the assembling of C 3B 2H 4 units have been constructed. At the B3LYP/6-311++G** and MP2/6-31G** levels of theory, these ptC compounds were predicted to be stable and they generally have large HOMO–LUMO gaps. The IR characteristic bands arising from the symmetrical and asymmetrical stretching vibrations of C–ptC, the stretching vibrations of C–B and B–H as well as the breath vibration of the two three-membered rings of C 3B 2 appear at 1000, 1250, 1600, 2800, and 1700 cm −1, respectively. Calculations also show that these ptC molecules have strong aromaticities and the ptC atom obeys the octal rule. Furthermore, the derivatives C 3B 2H 2(COOH) 2 and tetra-C 3B 2H 2-16-crown-4 can serve as the chelate ligands and form stable complexes with uranyl.

THEORETICAL STUDY OF NEUTRAL AND IONIC SinO(n = 1-13) CLUSTERS

A systematic theoretical study of the structural properties and stabilities for neutral Si n O (n = 1-13) clusters and their ions has been carried out using the full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method and the Amsterdam Density Functional (ADF) program with TZ2P basis set in conjunction with self-consistent field (SCF). Their ionization potentials (IPs), electron affinities (EAs), dipole moments μ, constant volume heat capacity Cv are computed. Based on the Mulliken population analyses, it is found that part of electronic charge is transferred from the Si atoms into the oxygen atom. Compared with other structures, the adsorption structures with an edge or a surface O atom are more stable. Calculations also show that the Si n O clusters with larger HOMO–LUMO gap exhibit high stability.

Competition between mixing and segregation in bimetallic AgnRbnclusters (n= 2–10),

We found the minimum-energy structures of AgnRbn(n = 2–10) clusters by a combination of density functional theory (DFT) and taboo search global optimization. The global minimum geometry is mixed for n ≤ 4 and segregated, with a core-shell arrangement, for n > 4. There is a change in the nature of the bonding, from ionic to metallic, between n = 4 and n = 5. Although metallic bonding dominates at n > 4, large atomic charges (in the order of ±0.5) persist. These atomic charges (negative on the interior Ag atoms, positive on the surface Rb atoms) make AgnRbnclusters analogous to Zintl compounds and could prevent them from coalescing. This makes them intriguing potential building blocks for cluster-assembled materials. Ag4Rb4is relatively stable compared with other AgnRbnclusters; it has a nearly cubic shape, a large HOMO–LUMO gap (2 eV), and a highly ionic character with atomic charges equal to roughly ±1 au.

3 d transition metals: Which is the ideal guest for Si n ( [formula omitted]) cages?

The configurations, stability, and electronic structures of Si 15 and Si 16 cages with encapsulated 3 d transition metal atoms, M@Si 15 and M@Si 16 (M = Sc, Ti, V, Cr, Mn, Fe, Co, or Ni), have been investigated within the framework of all-electron density functional theory. The results show that Ti@Si 16 and Ti@Si 15 have the largest embedding energies in this series and relatively large HOMO–LUMO gaps. This suggests that the titanium atom is an ideal guest for Si n ( n = 15 , 16 ) cages as far as stability is concerned. The Mn atom is found to have a large spin moment even when encapsulated, while the spin moments of Ti, Cr, Fe, and Ni are entirely quenched upon doping into the Si 15 and Si 16 cage clusters.

Bonding and electronic structures in W@Au12AE complexes (AE= NO+, CO, BF, CN–, or BO–): analogies among ligands isoelectronic to carbon monoxide

A theoretical study on the geometries and electronic structures of W@Au(12)AE (AE=NO(+), BF, CN(-), or BO(-)) was carried out to gain insight into interactions between W@Au(12) and ligands isoelectronic with CO. The best configuration for the adsorption site is on-top type for all five complexes. After complexing with boron ligands (BF or BO(-)), the axial Au-W bond distance in W@Au(12) is lengthened notably, but NO(+) has the opposite effect on the axial Au-W bond. A charge transfer and energy decomposition analysis shows that the metal-ligand bonds have enhanced sigma-donation strength from NO(+) to BO(-). Furthermore, the A-E bond strength in the complexes becomes weaker with stronger pi-back-donation interactions. Finally, W@Au(12)CO has the largest HOMO-LUMO gap, making it the most stable in terms of kinetic stability.

Two three-dimensional silver(I) coordination architectures with pyridine-3,5-dicarboxylate: Luminescence and structural dependence on preparing conditions

The hydrothermal reactions of pyridine-3,5-dicarboxylic acid (H 2pydc) with AgNO 3 in the mixed solvent of acetonitrile and water with different ratios lead to the formation of two three-dimensional network complexes, [Ag 5(pydc) 2(CN)] n ( 1) and {[Ag 4(pydc) 2]CH 3CN} n ( 2), which have been characterized by IR, single-crystal X-ray diffraction and thermogravimetric analyses. It has been demonstrated that the ratio of acetonitrile and water have great effect on the structures of products. The high ratio of acetonitrile and water is favorable for the formation of complex 1, while the low volume ratio is propitious to complex 2. The luminescent properties of complex 1 and 2 have been further investigated, and show that the luminescence intensity of 2 is much stronger than that of 1 probably due to the direct metal–metal interactions and a larger HOMO–LUMO gap in complex 2.

AlnBi Clusters: Transitions Between Aromatic and Jellium Stability

An experimental and theoretical study of bismuth-doped aluminum clusters in the gas phase has revealed two particularly stable clusters, namely, Al(3)Bi and Al(5)Bi. We show that their electronic structure can be understood in terms of the aromatic and "Jellium" models, respectively. Negative ion photodetachment spectra provide a fingerprint of the electronic states in Al(n)Bi(-) (n = 1-5) anions, while theoretical investigations reveal the nature of the electronic orbitals involved. Together, the findings reveal that the all-metal Al(3)Bi cluster with 14 valence electrons is a cyclic, planar structure with a calculated large ionization potential of 7.08 eV, a low electron affinity of 1.41 eV, and a large gap of 1.69 eV between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gap). The Al(3)Bi cluster has molecular orbitals reminiscent of aromatic systems and is a neutral cluster with no need for counterion or ligand support. A slightly larger cluster, Al(5)Bi, has 20 valence electrons and is another highly stable compact structure with a calculated large ionization potential of 6.51 eV and a large HOMO-LUMO gap of 1.15 eV. This cluster's stability is rooted in a Jellium electronic shell closing. The formation of stable species using aromatic bonding allows us to extend the idea of cluster-assembled materials built out of stable clusters with Jellium shell closings (superatoms) to include ones involving aromatic building blocks.

Lowest-energy structures and photoelectron spectra of In nP n ( n = 1–12) clusters from density functional theory

Lowest-energy structures of In n P n ( n = 1–12) clusters have been determined from a number of structural isomers using all-electron density functional calculations. The In–P alternating hollow cage-like structures emerge at n = 7. Size-dependent cluster properties such as binding energy, HOMO–LUMO gaps, electron affinities, and photoelectron spectra have been computed and discussed. The simulated electron affinities and photoelectron spectra agree reasonably with experiments. With exceptionally low electron affinity and large HOMO–LUMO gap, In 3P 3 was identified as a magic-numbered cluster of relatively higher stability, in agreement with experimental observations.

Atomic size effect on the structures and stability of X 7M (X=Al and In;M=Si −,Ge −,N and P) clusters

Based on the density functional theory, geometric and electronic properties of X 7M (X=Al and In; M=Si −, Ge −, N and P) clusters are studied. The lowest-energy structures for Al 7Si −, Al 7Ge − and Al 7P are largely different from that of Al 7C −. The size effect of impurity atom on the structures and stability has been analyzed. In 7C − and In 7N are found to have the same geometry as Al 7C −, in which the host atoms form a cage with C 3 v symmetry with impurity atoms locating at the central site. A significantly large HOMO–LUMO gap, low-electron affinity, and high ionization potential are the characters of a magic cluster found for In 7N, which may have potential application in cluster-assembled materials.

A DFT study of the interaction between butein anion and metal cations (M = Mg 2+, Cr 2+, Fe 2+, and Cu 2+): Taking an insight into its chelating property

Butein, a chalcone compound isolated from Dalbergia odorifera T. Chen, can inhibit lipid peroxidation induced by metal cations through its chelating property. In order to give an insight into the chelate property of butein, the geometries and electronic properties of metal–butein complexes (M = Mg 2+, Cr 2+, Fe 2+, and Cu 2+) are investigated by using density functional theory method in this paper. The natural bond orbitals (NBO) are also calculated to analyze the charge transfer between the metal cations and butein anion. The results find that the oxygen atom of 2′ and 9 position is the favored coordination site for all metal cations both in gas phase and in water phase, and the sequence of binding strength is Cu 2+ > Cr 2+ > Fe 2+ > Mg 2+, which is accordance with the quantity of charges transferred from metal cation to butein ligand. In addition, the Cu 2+–butein complex has the lowest HOMO–LUMO gap, and the Fe 2+–O 2′O 9 complex has the largest HOMO–LUMO gap.

Probing the Electronic Structure of Early Transition-Metal Oxide Clusters: Polyhedral Cages of (V2O5)n- (n = 2−4) and (M2O5)2- (M = Nb, Ta)

Vanadium oxide clusters, (V2O5)n, have been predicted to possess interesting polyhedral cage structures, which may serve as ideal molecular models for oxide surfaces and catalysts. Here we examine the electronic properties of these oxide clusters via anion photoelectron spectroscopy for (V2O5)n(-) (n = 2-4), as well as for the 4d/5d species, Nb4O10(-) and Ta4O10(-). Well-resolved photoelectron spectra have been obtained at 193 and 157 nm and used to compare with density functional calculations. Very high electron affinities and large HOMO-LUMO gaps are observed for all the (V2O5)n clusters. The HOMO-LUMO gaps of (V2O5)n, all exceeding that of the band gap of the bulk oxide, are found to increase with cluster size from n = 2-4. For the M4O10 clusters, we find that the Nb/Ta species yield similar spectra, both possessing lower electron affinities and larger HOMO-LUMO gaps relative to V4O10. The structures of the anionic and neutral clusters are optimized; the calculated electron binding energies and excitation spectra for the global minimum cage structures are in good agreement with the experiment. Evidence is also observed for the predicted trend of electron delocalization versus localization in the (V2O5)n(-) clusters. Further insights are provided pertaining to the potential chemical reactivities of the oxide clusters and properties of the bulk oxides.

Density Functional Theory Study of Structure and Electronic Properties of MgBen(n=212) Clusters

Determinations of the lowest energy structures and electronic properties of MgBen (n=2-12) clusters were carried out by using density-functional theory. It was found that MgBe3 and MgBe9 clusters with higher binding energy and larger HOMO-LUMO gap are more stable than the neighboring clusters. The electronic properties from van der Waals to covalent and bulk metallic behavior in MgBen (n=2-12) clusters are discussed with the evolution of the size, and the data indicates Magnesium-doped Beryllium clusters already early appear some metallic-like features than host Ben clusters. By analyzing electronic properties of MgBen (n=2-12) clusters, it can be concluded that Mg-doped reduces the stabilities of Be clusters.

Structures and Stabilities of Clusters of Si12, Si18, and Si20 Containing Endohedral Charged and Neutral Atomic Species

Electronic structure calculations based on density functional theory and Moller Plesset perturbation theory were performed on three isomers of Si 12 and on the endohedral clusters Si 12 containing neutral or charged atomic species. The existence of endohedral clusters depends on the Si 12 cage shape and the nature of the embedding species. Endohedral clusters of Li 0 ' 1 ' -1 , Na 0,1,-1 and He in Si 12 cages were found. In contrast, K + , Ne, F - , or Cl - do not form endohedral clusters with Si 12 due to their large size. All endohedral clusters that are minima on the potential energy surfaces are stable and have large HOMO-LUMO gaps (>1 eV). The stability order for the lithium and sodium clusters is: anionic clusters > neutral clusters > cationic clusters. The endohedral complex of two Li atoms with the Si 18 cage is lower in energy than the sum of the empty Si 18 cage and two Li atoms. In contrast, doping two Na atoms into the Si 18 cage forms an exohedral Na 2 Si 18 cluster. An endohedral cluster of Li 2 with Si 20 was also investigated and characterized. The stability of the endohedral complexes of two Li atoms in Si 18 and Si 20 suggest that silicon nanotubes, which are unstable, might be stabilized by an internal string of Li atoms.

Al7Ag and Al7Au Clusters with Large Highest Occupied Molecular Orbital−Lowest Unoccupied Molecular Orbital Gap

The candidate structures for the ground-state geometry of the Al(7)M (M = Li, Cu, Ag, and Au) clusters are obtained within the spin-polarized density functional theory. Absorption energy, vertical ionization potential, vertical electron affinity, and the energy gap between the highest occupied molecular orbital (HOMO) level and the lowest unoccupied molecular orbital (LUMO) level have been calculated to investigate the effects of doping. Doping with Ag or Au can lead to a large HOMO-LUMO gap, low electron affinity, and increased ionization potential of Al(7) cluster. In the lowest-energy structure of the Al(7)Au cluster, the Al atom binding to the Al(6)Au acts monovalent and the other six Al atoms are trivalent. Thus, the Al(7)Au cluster has 20 valence electrons, and its enhanced stability may be due to the electronic shell closure effect.

Evolution of the electronic structure and properties of neutral and charged cobalt-doped aluminum clusters

Structural and electronic properties of neutral and ionic Al n Co ( n = 8–17) clusters have been investigated by performing density-functional theory calculations within the effective core potential level. The total energies of these clusters are then used to study the evolution of their binding energy, relative stability, ionization potential, and vertical and adiabatic electron affinities as a function of size. Unlike the alkali atom-doped aluminum clusters in the same size range, the most cobalt atom resides inside the aluminum cluster cage except for Al 12Co, Al 13Co, Al 11Co −, Al 11Co + and Al 13Co + clusters. Furthermore, the 3d and 4s energy levels of Co hybridize with the valence electrons of Al causing a redistribution of the molecular orbital energy levels of the Al n clusters. The binding energy evolves monotonically with size, but Al 13Co, Al 13Co − and Al 13Co + exhibit greater stability than their neighbors, which is consistent with the large HOMO–LUMO gaps. The calculated results agree reasonable with all available experimental data on ionization energies and electron affinities.

Systematic search for energetically favored isomers of large fullerenes C122–C130 and C162–C180

Abstract Based on the methodology by Cioslowski et al. [J. Cioslowski, N. Rao, D. Moncrieff, J. Am. Chem. Soc. 122 (2000) 8265–8270], two empirical fit equations to predict the standard enthalpy of formation are obtained over large number of calculation results at B3LYP/6-31G* theory level for fullerene isomers, which can be used as a preliminary and second-level screening tool, respectively, for large fullerenes. By applying these equations in screening the whole isolated pentagon rule (IPR) isomers, the energetically favored isomers of large fullerenes C 122 –C 130 and C 162 –C 180 were predicted at the B3LYP/6-31G* density functional theory level for the first time. Our results show that the lowest energy isomers of C 174 (2473259: C 3 v ) and C 180 (4071832: I h ) possess much lower relative energy and larger HOMO–LUMO gaps. Moreover, the ionization energy and electron affinity of the lowest energy isomers were also investigated.

Structural and electronic properties of a trimetallic nanoparticle catalyst: Ru 5PtSn

Density functional theory is used to explore the trimetallic nanoparticle catalyst Ru 5PtSn. Results are presented for the catalyst precursor PtRu 5(CO) 15(μ-SnPh 2)(μ 6-C), as well as for Ru 5PtCSn and Ru 5PtSn in the gas phase and for Ru 5PtCSn supported on the (0 0 1) face of α-christobalite. Removal of the ligands introduces marked structural relaxations in the metal core. Whereas, the ligand-stabilized system has a large HOMO–LUMO gap, such a separation is not present for Ru 5PtCSn and Ru 5PtSn. Ru 5PtCSn is predicted to be anchored to the α-christobalite surface via Ru O bonds.