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1.
Based on experimental zinc blende and wurtzite models of CdSe nanocrystals, four clusters of CdSe, seven Se-Cd-ligand structures,
and their characters are studied at DFT/B3LYP/Lanl2dz theoretical level. Cd3Se3, (Cd3Se3)2 and (Cd3Se3)3 clusters which have a ring with six atoms are similar to wurtzite structures, Cd4Se4 have resemblant conformation with zinc blende for they are all composed of tetrahedron. Calculated Raman spectra of Cd3Se3, Cd4Se4, (Cd3Se3)2 and (Cd3Se3)3 are about 175 cm−1 which is consistent with the experimental result. Then, through investigation of Se-Cd-ligand clusters, we find that all
Se-Cd-ligand structures have similar characters because main influence of ligands on nanocrystals comes from thiol. Finally,
we testify that both solvent and ligand make absorption peaks shift to blue, compared with those in gas phase and without
ligand. Under these conditions, calculated data of four clusters are almost identical with the absorption peaks of CdSe nanocrystals.
Besides, we also prove that the absorption peaks of four clusters are the transitions from HOMO to LUMO or from d to p orbitals.
And HOMO-LUMO gaps reduce in order of Cd3Se3, (Cd3Se3)2 and (Cd3Se3)3, which is induced by the quantum size effect. 相似文献
2.
Vapor phase transport (VPT) assisted by mixture of methanol and acetone via thermal evaporation of brass (CuZn) was used to prepare un-doped and Al-doped zinc oxide (ZnO) nanostructures (NSs). The structure and morphology were characterized by field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD). Photoluminescence (PL) properties of un-doped and Al-doped ZnO showed significant changes in the optical properties providing evidence for several types of defects such as zinc interstitials (Zni), oxygen interstitials (Oi), zinc vacancy (Vzn), singly charged zinc vacancy (VZn
-), oxygen vacancy (Vo), singly charged oxygen vacancy (Vo
+) and oxygen anti-site defects (OZn) in the grown NSs. The Al-doped ZnO NSs have exhibited shifted PL peaks at near band edge (NBE) and red luminescence compared to the un-doped ZnO. The Raman scattering results provided evidence of Al doping into the ZnO NSs due to peak shift from 145 cm-1 to an anomalous peak at 138 cm-1. Presence of enhanced Raman signal at around 274 and 743 cm-1 further confirmed Al in ZnO NSs. The enhanced D and G band in all Al-doped ZnO NSs shows possible functionalization and doping process in ZnO NSs. 相似文献
3.
The intermolecular interactions between Aun (n = 3–4) clusters and selected amino acids cysteine and glycine have been investigated by means of density functional theory
(DFT). Present calculations show that the complexes possessing Au-NH2 anchoring bond are found to be energetically favored. The results of NBO and frontier molecular orbitals analysis indicate
that for the complex with anchoring bonds, lone pair electrons of sulfur, oxygen, and nitrogen atoms are transferred to the
antibonding orbitals of gold, while for the complex with the nonconventional hydrogen bonds (Au···H–O), the lone pair electrons
of gold are transferred to the antibonding orbitals of O-H bonds during the interaction. Furthermore, the interaction energy
calculations show that the complexes with Au-NH2 anchoring bond have relatively high intermolecular interaction energy, which is consistent with previous computational studies. 相似文献
4.
Li-Ping Ding Xiao-Yu Kuang Peng Shao Ming-Min Zhong 《Journal of molecular modeling》2013,19(4):1527-1536
The structural, electronic and magnetic properties of neutral and anion Fe2S2, Fe3S4 and Fe4S4 have been investigated with the aid of previous photoelectron spectroscopy and density functional theory calculations. Theoretical electron detachment energies (both vertical and adiabatic) of anion clusters for the lowest energy structure were computed and compared with the experimental results to verify the ground states. The optimized structures show that the ground state structures of Fe2S2 0/?, Fe3S4 0/? and Fe4S4 0/? favor high spin state and are similar to their structures in proteins. The electron delocalization pattern for all the clusters and the nature of bonding between Fe and S atoms were studied by analyzing molecular orbitals. Natural population analysis demonstrates that Fe atoms act as an electron donor in all clusters, and the electron density difference map clearly shows the direction of the electron flow over the whole complex. Furthermore, the investigated magnetism shows that the Fe atoms carried most of the magnetic moments, which is due mainly to the 3d state, while only very small magnetic moments are found on S atoms. 相似文献
5.
The structures of ZnO graphene–like nanosheets (ZnOGLNS), i.e., ZnO aromatic–like (AL–ZnONS), naphthalene–like (NLL–ZnONS),
pyrene–like (PRL–ZnONS), coronene–like (CNL–ZnONS) and circumcoronene–like (CCL–ZnONS) and their oxygen adsorptions were obtained
using the B3LYP/LanL2DZ method. Adsorption energies of O2 on AL–ZnONS, NLL–ZnONS, PRL–ZnONS, CNL–ZnONS and CCL–ZnONS are reported. The bond strengths of the most inner Zn–O bonds
of ZnOGLNSs are in order: CCL–ZnONS > CNL–ZnONS > PRL–ZnONS. It was found that chemisorptions of O2 occur on the hydride atoms of zinc–hydride in the ZnOGLNSs. Physisorptions of O2 only occurring over the plane of ZnOGLNS were found. All the ZnOGLNSs are oxygen sensitive materials and would be developed
to be oxygen sensor based on electrical conductivity. 相似文献
6.
The stable geometries and atomization energies for the clusters Ni
n
(n = 2–5) are predicted with all-electron density functional theory (DFT), using the BMK hybrid functional and a Gaussian basis
set. Possible isomers and several spin states of these nickel clusters are considered systematically. The ground spin state
and the lowest energy isomers are identified for each cluster size. The results are compared to available experimental and
other theoretical data. The molecular orbitals of the largest cluster are plotted for all spin states. The relative stabilities
of these states are interpreted in terms of superatom orbitals and no-pair bonding. 相似文献
7.
Tadeusz M. Krygowski Wojciech P. Oziminski Christopher A. Ramsden 《Journal of molecular modeling》2011,17(6):1427-1433
The reasons behind changes of aromaticity in 10 unsubstituted aza-azoles were analysed by employing the natural bond orbital
(NBO) approach at the MP2/6-311+G(d,p) level of theory. Sum of occupations of p
z
orbitals at atoms in the ring correlates well with the magnetism based aromaticity index NICS as well as with the number
of nitrogen atoms in the ring. Changes of NICS depend strongly in a linear way on the number of NN bonds. Classification of
azoles based on the number of pyridine-type nitrogen atoms vicinal to NH is supported by plotting the relative occupation
of π orbitals (πocc) against the relative occupation of σ orbitals (σocc) for all individual atoms in rings. 相似文献
8.
Geometrical structures and relative stabilities of (LiNH2)n (n = 1–5) clusters were studied using density functional theory (DFT) at the B3LYP/6-31G* and B3LYP/6-31++G* levels. The electronic
structures, vibrational properties, N–H bond dissociation energies (BDE), thermodynamic properties, bond properties and ionization
potentials were analyzed for the most stable isomers. The calculated results show that the Li–N and Li–Li bonds can be formed
more easily than those of the Li–H or N–H bonds in the clusters, in which NH2 is bound to the framework of Li atomic clusters with fused rings. The average binding energies for each LiNH2 unit increase gradually from 142 kJ mol−1 up to about 180 kJ mol−1 with increasing n. Natural bond orbital (NBO) analysis suggests that the bonds between Li and NH2 are of strong ionicity. Three-center–two-electron Li–N–Li bonding exists in the (LiNH2)2 dimer. The N–H BDE values indicate that the change in N–H BDE values from the monomer a1 to the singlet-state clusters is small. The N–H bonds in singlet state clusters are stable, while the N–H bonds in triplet
clusters dissociate easily. A study of their thermodynamic properties suggests that monomer a1 forms clusters (b1, c1, d2 and e1) easily at low temperature, and clusters with fewer numbers of rings tend to transfer to ones with more rings at low temperature.
E
g, E
HOMO and E
av decrease gradually, and become constant. Ring-like (LiNH2)3,4 clusters possess higher ionization energy (VIE) and E
g, but lower values of E
HOMO. Ring-like (LiNH2)3,4 clusters are more stable than other types. A comparison of structures and spectra between clusters and crystal showed that
the NH2 moiety in clusters has a structure and spectral features similar to those of the crystal. 相似文献
9.
《Inorganica chimica acta》1986,116(2):109-117
Previously developed methods for the treatment of polyhedral boranes, carboranes, and metal clusters are extended to the treatment of gold clusters, which present a variety of new problems. In most cases gold atoms in such cluster compounds do not employ the usual 9-orbital sp3d5 spherical bonding orbital manifold. Instead almost all non-tetrahedral gold clusters consist of a center gold atom surrounded by a puckered polygonal belt of peripheral gold atoms generally with one or more additional peripheral gold atoms in distal positions above and/or below the belt. The peripheral gold atoms in such clusters use a 7-orbital spd5 cylindrical bonding orbital manifold, but their residual two orthogonal anti- bonding p orbitals can receive electron density from the filled d orbitals of adjacent peripheral gold atoms through dσ → pσ* and/or dπ → pπ* backbonding leading to bonding distances between adjacent peripheral gold atoms. Centered gold clusters can be classified into either spherical or toroidal clusters depending upon whether the center gold atom uses a 9-orbital sp3d5 spherical bonding orbital manifold or an 8-orbital sp2d5 toroidal bonding orbital manifold, respectively. The topology of the core bonding in gold clusters is generally not that of the Kn complete graph found in other clusters but instead mimics the topology of the polyhedron formed by the surface atoms. This apparently is a consequence of the poor lateral overlap of the cylindrical spd5 manifolds of the peripheral gold atoms. Examples of non-centered gold clusters treated in this paper include the squashed pentagonal bipyramidal Au7(PPh3)7+ and the edge-fused bitetrahedral (Ph3P)4Au6[Co(CO)4]2 which may be regarded as a ‘perauraethylene’ in which the six cluster gold atoms correspond to the six atoms of ethylene including a double bond between the two gold atoms corresponding to the two ethylene carbon atoms. 相似文献
10.
The effects of ultrafine and fine particles of zinc oxide (ZnO) on IgE-dependent mast cell activation were investigated. The
rat mast cell line RBL2H3 sensitized with monoclonal anti-ovalbumin (OVA) IgE was challenged with OVA in the presence or absence
of ZnO particles and zinc sulfate (ZnSO4). Degranulation of RBL2H3 was examined by the release of β-hexosaminidase. To understand the mechanisms responsible for regulating
mast cell functions, the effects of ZnO particles on the levels of intracellular Zn2+, Ca2+, phosphorylated-Akt, and global tyrosine phosphorylation were also measured. IgE-induced release of β-hexosaminidase was
obviously attenuated by ultrafine ZnO particles and ZnSO4, whereas it was very weakly inhibited by fine ZnO particles. The intracellular Zn2+ concentration was higher in the cells incubated with ultrafine ZnO particles than in those with fine ZnO particles. Consistent
with inhibitory effect on release of β-hexosaminidase, ultrafine ZnO particles and ZnSO4, but not fine ZnO particle, strongly attenuated the IgE-mediated increase of phosphorylated-Akt and tyrosine phosphorylations
of 100 and 70 kDa proteins in RBL2H3 cells. These findings indicate that ultrafine ZnO particles, with a small diameter and
a large total surface area/mass, could release Zn2+ easily and increase intracellular Zn2+ concentration efficiently, thus decreasing FcεRI-mediated mast cell degranulation through inhibitions of PI3K and protein
tyrosine kinase activation. Exposure to ZnO particles might affect immune responses, especially in allergic diseases. 相似文献
11.
The question whether Au can alloy with Pt at the nano-scale size is still controversial. By performing density functional
theory calculations for several small Au/Pt bimetallic clusters AumPtn (m + n = 4–6, 13), we find that, in all the most stable geometries, Pt atoms prefer to assemble together to form the core
while Au atoms like to surround the Pt atoms to form the shell, and that evenly mixed clusters are structurally unstable.
The unique geometric characteristics can be explained by analyzing the different electronic properties of Pt–Pt, Au–Pt and
Au–Au bonds, and is expected also to apply to larger Au/Pt bimetallic clusters. 相似文献
12.
Abdeladim Guermoune Al Mokhtar Lamsabhi Driss Cherqaoui Abdellah Jarid Hafid Anane Gabriel Merino 《Journal of molecular modeling》2010,16(3):551-557
The stability of the tri–μ–hydrido–bis[(η5–C5Me5)aluminum], Cp*2Al2H3, 1 is studied at B3LYP/6–311+G(d,p), CCSD(T)//B3LYP/6–311+G(d,p) and MP4//B3LYP/6–311+G(d,p) levels. The coordination between
Al2H3 entity and both C5(CH3)5 groups is ensured by strong electrostatic and orbital interactions. The orbital analysis of the interacting fragments shows
that Al2H3 acceptor, which keeps its tribridged structure, implies the vacant
( \texta1¢ ) \left( {{\text{a}}_1^\prime } \right) and five antibonding (a2¢¢ a_2^{\prime \prime } , e′ and e″) molecular orbitals to interact with two orbitals mixtures, b1 and e" of the donors (C5Me5). When we take into account the solvent effect, the computation shows that 1 seems to be stable in condensed phase with a tribridged bond between the Al atoms [Cp*Al(μ-H)3AlCp*], whereas in the gas phase, the monobridged Cp*AlH(μ-H)AlHCp* 4 is slightly favored (4 kcal mol−1). We propose that 1 could be prepared thanks to Cp*Al (2) and Cp*AlH2 (3) reaction in acidic medium. The experimental treatment of this type of metallocenes would contribute to the development of
the organometallic chemistry of 13th group elements.
相似文献
13.
Saeed Aslanzadeh 《Journal of molecular modeling》2016,22(7):160
Metal doped ZnO nanomaterials have attracted considerable attention as a chemical sensor for toxic gases. Here, the electronic sensitivity of pristine and Sc-, Ti-, V-, Cr-, Mn-, and Fe-doped Zn12O12 nanoclusters toward CO gas is investigated using density functional theory calculations. It is found that replacing a Zn atom by a Sc or Ti atom does not change the sensitivity of cluster but doping V and Cr atoms significantly increase the sensitivity. Also, Mn, or Fe doping slightly improves the sensitivity. It is predicted that among all, the Cr-doped ZnO cluster may be the most favorable sensor for CO detection because its electrical conductivity considerably changes after the CO adsorption, thereby, generating an electrical signal. The calculated Gibbs free energy change for the adsorption of CO molecule on the Cr-doped cluster is about -51.2 kcal mol-1 at 298.15 K and 1 atm, and the HOMO-LUMO gap of the adsorbent is changed by about 117.8 %. 相似文献
14.
A first-principle investigation of structures and properties of Ni n Pd n (n=1-5) clusters is presented. For this study, the linear combination of Gaussian-type orbitals auxiliary density functional theory (LCGTO-ADFT) method has been employed. In order to determine the lowest energy structures, several isomers in different spin multiplicities were studied, for each cluster size. Initial structures, for which successive geometry optimization was computed without any constrain, were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories. To discriminate between minima and transition state structures, harmonic frequency analyses were performed at the optimized structures. Ground state structures, bond lengths, harmonic frequencies, dissociation energy, ionization potential, electron affinity and spin density plots are presented. This work demonstrates, that the Pd atoms prefer to allocate on the surface of the cluster structures whose core is formed by the 3d TM atoms type. Moreover, it has been observed that the ground-state structure spin multiplicity increases as the system size grows. The results of this study contribute to gain insight into how structures and energy properties change with cluster size in bimetallic Pd-based alloys. 相似文献
15.
Density functional theory (DFT) calculations were performed to study doping of two nitrogen atoms at different positions on a finite-sized graphene model of C82H24. We examined 21 structures of double nitrogen doped graphene to calculate their relative stabilities. The structure with two nitrogen atoms located apart is the most stable among the positional isomers considered in this study. For double nitrogen doping within a six-membered ring, the 1,4-position is more preferred than 1,3- or 1,2-positions for the finite-sized single layer graphene sheet. Our computational study supports the experimental observation of two nitrogen atoms at the 1,3- and 1,4-positions in a single six-membered ring of graphene. Furthermore, the structures with N-N bond are the least stable among two nitrogen doped graphene structures. The effects of nitrogen doping and the positions of two nitrogen atoms on the HOMO-LUMO energy gap of pristine graphene were analyzed. 相似文献
16.
The molecular geometries, vibrational properties, and thermodynamic properties of the clusters (Br2GaN3)
n
(n = 1–4) were studied at the B3LYP/6-311+G* level. The optimized clusters (Br2GaN3)
n
(n = 2–4) were all found to possess a cyclic structure consisting of Ga atoms bridged by the α-nitrogen of the azide groups.
A discussion of the relationships between the geometrical parameters and the degree of oligomerization n is provided. Features in the IR spectra were assigned by vibrational analysis. Trends in thermodynamic properties with temperature
and degree of oligomerization n are discussed. Thermodynamic analysis of the gas-phase reaction showed that the formation of the clusters (Br2GaN3)
n
(n = 2–4) is thermodynamically favorable considering the enthalpies at 298.2 K. The calculated results for the Gibbs free energies
were negative, which indicates that the oligomerizations can occur spontaneously at 298.2 K. 相似文献
17.
The local meta-GGA exchange correlation density functional (TPSS) with a relativistic effective core potential was employed
to systematically investigate the geometric structures, stabilities, and electronic properties of bimetallic Ca2Au
n
(n = 1–9) and pure gold Au
n
(n ≤ 11) clusters. The optimized geometries show that the most stable isomers for Ca2Au
n
clusters have 3D structure when n > 2, and that one Au atom capping the Ca2Au
n−1 structure for different-sized Ca2Au
n
(n = 1–9) clusters is the dominant growth pattern. The average atomic binding energies and second-order difference in energies
show that the Ca2Au4 isomer is the most stable among the Ca2Au
n
clusters. The same pronounced even–odd alternations are found in the HOMO–LUMO gaps, VIPs, and hardnesses. The polarizabilities
of the Ca2Au
n
clusters show an obvious local minimum at n = 4. Moreover, the inverse corrections to the polarizabilities versus the ionization potential and hardness were found for
the gold clusters. 相似文献
18.
The present study reports the geometry, electronic structure and properties of neutral and anionic transition metal (TM =
Ti, Zr and Hf)) doped germanium clusters containing 1 to 20 germanium atoms within the framework of linear combination of
atomic orbitals density functional theory under spin polarized generalized gradient approximation. Different parameters, like,
binding energy (BE), embedding energy (EE), energy gap between the highest occupied and lowest unoccupied molecular orbitals
(HOMO-LUMO), ionization energy (IP), electron affinity (EA), chemical potential etc. of the energetically stable clusters
(ground state cluster) in each size are calculated. From the variation of these parameters with the size of the clusters the
most stable cluster within the range of calculation is identified. It is found that the clusters having 20 valence electrons
turn out to be relatively more stable in both the neutral and the anionic series. The sharp drop in IP as the valence electron
count increases from 20 to 21 in neutral cluster is in agreement with predictions of shell models. To study the vibrational
nature of the clusters, IR and Raman spectrum of some selected TM@Gen (n = 15,16,17) clusters are also calculated and compared. In the end, relevance of calculated results to the design of Ge-based
super-atoms is discussed. 相似文献
19.
The formation of protein clusters or a protein-rich phase in undersaturated solutions of biopolymers is considered theoretically
on the basis of phase diagrams of a water-protein-salt system. Concentrated (50–200 mg/ml of protein) water-salt solutions
of human serum albumin molecules modified by a maleimide spin-label have been studied experimentally using the ESR technique
to characterize the significant general features of the system behaviour suggested by the model phase diagrams. The inorganic
ion content (NaCl, KSCN, MgCl2, and CaCl2) was varied in the range of 10−3–4 M. Salt-induced changes in different experimental ESR spin-label parameters based on relations between spectral line widths
and amplitudes were determined and compared with the same parameters in salt-free solution. The data on dipole-dipole interactions
of spin labels obtained at 77 K and on spin exchange at normal temperatures are indicative of local protein concentration
inhomogeneities. The results have been described in terms of salt-induced dissociation of stabilized supramolecular structures
in protein solution–protein clusters, liquid-liquid phase transition between the hydration water of clusters and that of individual
proteins, and a rise in surface tension which results in protein stabilization.
Received: 22 December 1998 / Revised version: 23 August 1999 / Accepted: 24 September 1999 相似文献
20.
Ab initio methods based on density functional theory at BP86 level were applied to the study of the geometrical structures,
relative stabilities, and electronic properties of small bimetallic Be2Au
n
(n = 1–9) clusters. The optimized geometries reveal that the most stable isomers have 3D structures at n = 3, 5, 7, 8, and 9. Here, the relative stabilities were investigated in terms of the averaged atomic binding energies, fragmentation
energies and second-order difference of energies. The results show that the planar Be2Au4 structure is the most stable structure for Be2Au
n
clusters. The HOMO−LUMO gap, vertical ionization potential, vertical electron affinity and chemical hardness exhibit a pronounced
even–odd alternating phenomenon. In addition, charge transfer and natural electron configuration were analyzed and compared. 相似文献