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1.
A modified adaptive immune optimization algorithm (AIOA) is designed for optimization of Cu–Au and Ag–Au bimetallic clusters with Gupta potential. Compared with homoatom clusters, there are homotopic isomers in bimetallic cluster, so atom exchange operation is presented in the modified AIOA. The efficiency of the algorithm is tested by optimization of CunAu38‐n (0 ≤ n ≤ 38). Results show that all the structures with the putative global minimal energies are successfully located. In the optimization of AgnAu55‐n (0 ≤ n ≤ 55) bimetallic clusters, all the structures with the reported minimal energies are obtained, and 36 structures with even lower potential energies are found. On the other hand, with the optimized structures of CunAu55‐n, it is shown that all 55‐atom Cu–Au bimetallic clusters are Mackay icosahedra except for Au55, which is a face‐centered cubic (fcc)‐like structure; Cu55, Cu12Au43, and Cu1Au54 have two‐shell Mackay icosahedral geometries with Ih point group symmetry. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 相似文献
2.
Spectral characteristics of (H2O)n, (O2)m(H2O)n, and (O)i(H2O)n cluster systems, where m≤2, i≤4, and 10 ≤ n ≤ 50, are studied with the molecular dynamics method using a flexible molecule model. The IR absorption spectra are changed substantially as a result of O2 molecule dissociation, and in the presence of atomic oxygen in the clusters, the spectra are characterized by a deep minimum at 520 cm?1. The absorption of oxygen causes a marked reduction in reflection coefficient R of monochromatic IR radiation. The number of peaks in the R(ω) spectra decreases to two in the case of molecular oxygen absorption and is no larger than four in the case of atomic oxygen absorption. The absorption of atomic oxygen by the clusters is also accompanied by a significant increase in the dissipation of energy accumulated by the clusters. This effect weakens when molecular oxygen is absorbed. An increase in atomic oxygen concentration in the clusters renders their radiation harder. 相似文献
3.
Shuang Zhao YunLai Ren WeiWei Lu YunLi Ren JianJi Wang WeiPing Yin 《Journal of Cluster Science》2012,23(4):1039-1048
Density functional theory calculations were performed to investigate the structural and energetic properties of NO2 adsorption on small bimetallic Ag n Cu m clusters (n?+?m?≤?5). Generally NO2 is adsorbed in bridge configuration. The adsorbates prefer Cu sites when both Ag and Cu co-exist in the clusters. The adsorption energies and the dissociation energies of the complex clusters increase as the Cu content increases for the given cluster size. Our calculation suggests that the bimetallic Ag n Cu m may react with NO2 dissociatively by way of Ag atom, Ag2 or AgCu loss. The N–O vibrational properties of the complex clusters were also discussed and analyzed. 相似文献
4.
Tobias F. Pascher Dr. Milan Ončák Dr. Christian van der Linde Prof. Dr. Martin K. Beyer 《ChemistryOpen》2019,8(12):1453-1459
The decomposition of copper formate clusters is investigated in the gas phase by infrared multiple photon dissociation of Cu(II)n(HCO2)2n+1−, n≤8. In combination with quantum chemical calculations and reactivity measurements using oxygen, elementary steps of the decomposition of copper formate are characterized, which play a key role during calcination as well as for the function of copper hydride based catalysts. The decomposition of larger clusters (n > 2) takes place exclusively by the sequential loss of neutral copper formate units Cu(II)(HCO2)2 or Cu(II)2(HCO2)4, leading to clusters with n=1 or n=2. Only for these small clusters, redox reactions are observed as discussed in detail previously, including the formation of formic acid or loss of hydrogen atoms, leading to a variety of Cu(I) complexes. The stoichiometric monovalent copper formate clusters Cu(I)m(HCO2)m+1−, (m=1,2) decompose exclusively by decarboxylation, leading towards copper hydrides in oxidation state +I. Copper oxide centers are obtained via reactions of molecular oxygen with copper hydride centers, species containing carbon dioxide radical anions as ligands or a Cu(0) center. However, stoichiometric copper(I) and copper(II) formate Cu(I)(HCO2)2− and Cu(II)(HCO2)3−, respectively, is unreactive towards oxygen. 相似文献
5.
6.
Tobias F. Pascher Dr. Milan Ončák Dr. Christian van der Linde Prof. Dr. Martin K. Beyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(37):8286-8295
The electronic structure and photochemistry of copper formate clusters, CuI2(HCO2)3− and CuIIn(HCO2)2n+1−, n≤8, are investigated in the gas phase by using UV/Vis spectroscopy in combination with quantum chemical calculations. A clear difference in the spectra of clusters with CuI and CuII copper ions is observed. For the CuI species, transitions between copper d and s/p orbitals are recorded. For stoichiometric CuII formate clusters, the spectra are dominated by copper d–d transitions and charge-transfer excitations from formate to the vacant copper d orbital. Calculations reveal the existence of several energetically low-lying isomers, and the energetic position of the electronic transitions depends strongly on the specific isomer. The oxidation state of the copper centers governs the photochemistry. In CuII(HCO2)3−, fast internal conversion into the electronic ground state is observed, leading to statistical dissociation; for charge-transfer excitations, specific excited-state reaction channels are observed in addition, such as formyloxyl radical loss. In CuI2(HCO2)3−, the system relaxes to a local minimum on an excited-state potential-energy surface and might undergo fluorescence or reach a conical intersection to the ground state; in both cases, this provides substantial energy for statistical decomposition. Alternatively, a CuII(HCO2)3Cu0− biradical structure is formed in the excited state, which gives rise to the photochemical loss of a neutral copper atom. 相似文献
7.
An all-electron scalar relativistic calculation on Cu
n
H (n = 1–13) clusters has been performed by using density functional theory with the generalized gradient approximation at the
PW91 level. Our results reveal that the hydrogen atom prefers to occupy the two fold coordination site for Cu
n
H (n = 2, 4–6, 8, 10–13) clusters, the single fold coordination site for Cu
n
H (n = 1, 3, 7) and the three fold coordination site for Cu9H cluster. For all Cu
n
H clusters, only the Cu11 structure in Cu11H is distorted obviously. After adsorption, the Cu–Cu bond is strengthened and the Cu–H bond of odd-numbered Cu
n
H clusters is relatively stronger than that of adjacent even-numbered Cu
n
H clusters. The Cu–Cu bond-length and Cu–H bond-length for all Cu
n
H clusters of our work are significantly shorter than those of previous work. This discrepancy can be explained in terms of
the scalar relativistic effect. The most favorable adsorption between small copper clusters and hydrogen atom takes place
in the case that hydrogen atom is adsorbed onto an odd-numbered pure Cu
n
cluster and becomes Cu
n
H cluster with even number of valence electrons. The odd–even alteration of magnetic moments is observed in Cu
n
H clusters and may provide the material with tunable code capacity of “0” and “1” by adsorbing a hydrogen atom onto odd- or
even-numbered copper clusters. 相似文献
8.
Hisayoshi Kobayashi Katsumi Nakashiro Tomoatsu Iwakuwa 《Theoretical chemistry accounts》1999,102(1-6):237-243
The mechanism of ethylene epoxidation on Ag surfaces has been investigated using the density functional method and Ag
n
clusters (n = 3 to 10) modeling the Ag(111) surface. The adsorption energy of O2 to the Ag clusters was strongly dependent on the HOMO level of the cluster, and the clusters with higher HOMO levels afforded
larger O2 adsorption energies. The energetics was investigated for both the molecular and atomic oxygen epoxidation mechanisms. For
the atomic oxygen mechanism, epoxidation was found to proceed without an activation energy, whereas a small amount of activation
energy (about 5 kcal/mol) was calculated for the molecular oxygen mechanism.
Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999 相似文献
9.
Eisaku Miyoshi Hiroshi Tatewaki Takashi Nakamura 《International journal of quantum chemistry》1983,23(4):1201-1207
An all-electron ab initio LCAO -MO SCF calculation has been carried out for the electronic structure of small copper clusters (Cun, n = 2–6). The basis set superposition error occurring in the calculation, the equilibrium configuration of Cu3, the bond energy in the clusters, and the localized d-hole in excited and ionized states of Cu2 are closely examined. 相似文献
10.
O. A. Novruzova 《Russian Journal of General Chemistry》2006,76(11):1698-1704
The IR absorption and reflection spectra of aqueous dispersions consisting of (H2O)n, O2(H2O)n, and (O2)2(H2O)n clusters (10 ≤ n ≤ 50) were calculated by the method of molecular dynamics using a flexible model of molecules. The frequency distribution of the power scattered by the cluster systems was obtained in the range 0 ≤ ω ≤ 3000 cm?1. The capture of one oxygen molecule by the clusters is accompanied by a decrease in the absorption of the low-frequency IR radiation and by a peak of the absorption intensity in the vicinity of ω 2704 cm?1. This is also accompanied by a decrease in the reflection coefficient throughout the frequency range and a decrease in the emission power at ω < 1030 and ω > 1700 cm?1. Addition of two oxygen molecules to the clusters decreases the capability of the dispersions for the absorption, reflection, and scattering of IR radiation. 相似文献
11.
V. V. Gogol’ D. A. Pichugina N. E. Kuz’menko 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(12):2402-2407
The interaction between carbon oxide and [Au20–nCun]q clusters (n = 0, 1, 19, 20 and q = 0, ±1) is studied by means of DFT/PBE in the scalar relativistic approximation. To establish the composition and structure of an adsorption site, isomers of bimetallic Au19Cu and AuCu19 particles with different positions of the heteroatom at an apex, edge, and face of the tetrahedral framework are considered. The optimized structures are used as the basis to determine the electronic properties of clusters (average bond energy per atom, difference of energies between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), ionization potential, electron affinity energy). The calculated parameters shrink as the copper content in clusters grows. Among the uncharged models, the highest CO adsorption energy is typical of Au19Cu, the heteroatom of which lies at a cluster’s apex. The CO adsorption energy for cationic and anionic clusters grows in comparison to neutral clusters. 相似文献
12.
The preferential oxidation (PROX, CO + H2 + O2 → CO2 + H2O) of the CO reaction in an H2 stream is the simplest and most cost-effective method to remove CO gas to less than 10 ppm in reformed fuel gas. We study the mechanism of PROX of the CO reaction in the H2 stream catalyzed by Cu n Ni (n = 3-12) clusters using a density functional theory (DFT) calculation to investigate bimetallic effects on the catalytic activation. Our results indicate that the Cu12Ni cluster is the most efficient catalyst for H2 dissociation and the Cu6Ni cluster is the most efficient catalyst for CO-PROX in excess hydrogen among Cu n Ni (n = 3-12) clusters. To gain insight into the adsorption and dissociation of the H2 molecule effect in the catalytic activity over the Cu12Ni cluster and the potential energy surfaces about PROX of CO oxidation on the Cu6Ni cluster, the nature of the interaction between the adsorbate and substrate is analyzed by detailed electron local densities of states (LDOS) as well as molecular structures. 相似文献
13.
Peter Lievens Peter Thoen Steven Bouckaert Wim Bouwen Erno Vandeweert Frederik Vanhoutte Horst Weidele Roger E. Silverans 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,42(3):231-235
We report on the production of small and medium size lithium and lithium oxide clusters by a laser vaporization cluster source. The isotopomeric distribution of natural lithium allowed to identify LikO clusters as the most abundant components in the mass spectrum. Photoionization efficiency curves of LikO clusters with photon energies from 3.4 to 4.7 eV were measured for 8 ≤ k ≤ 27. Using linear extrapolation of the increase in photoionization efficiency with photon energy, ionization potentials were extracted. With the chemical bond of the O2- anion to two Li atoms, leaving n = k-2 valence electrons in the (Li2O)Lin clusters, clear shell closure effects are present at n = 8 and n = 20. 相似文献
14.
Alexander Jakob Tobias Rüffer Petra Ecorchard Bernhard Walfort Kathrin Körbitz Swantje Frühauf Stefan E. Schulz Thomas Gessner Prof. Dr. Heinrich Lang 《无机化学与普通化学杂志》2010,636(11):1931-1940
Dicopper dicarboxylates [(R3P)mCuXCu(PR3)m] ( 5a , X = O2CCO2, R = Ph, m = 2; 5b , X = O2CCO2, R = nBu, m = 3) were prepared by treatment of [Cu2O] ( 1a ) with HO2CCO2H ( 2a ) in presence of PR3 ( 4a , R = Ph; 4b , R = nBu). A further synthesis approach to mono‐ and dicopper dicarboxylates is given using an electrolysis cell equipped with Cu electrodes and charged with acids H2X and phosphanes R3P. Without addition of a base mononuclear [(nBu3P)mCuXH] ( 6a , m = 3, XH = O2CCO2H, 6b , m = 3, XH = O2CCH2CO2H, 6c , m = 3, XH = O2CCH2CH2CO2H, 6d , m = 2, XH = O2C‐2‐C5H4N‐6‐CO2H) was formed, whereas in presence of NEt3 ( 3 ), the dicopper systems [(R3P)mCuXCu(PR3)m] ( 5a , X = O2CCO2, R = Ph, m = 2; 5b , X = O2CCO2, R = nBu, m = 3; 5c , X = O2CCH2CO2, R = nBu, m = 3; 5d , X = O2CCH2CH2CO2, R = nBu, m = 3; 5e , X = O2C‐2‐C5H4N‐6‐CO2, R = nBu, m = 3) were produced. When 6a reacted with [(tmeda)Zn(nBu)2] ( 7 ), trimetallic [(tmeda)Zn((nBu3P)3CuO2CCO2)2] ( 8 ) was accessible. In this heterobimetallic complex the Zn(tmeda) unit spans two CuO2CCO2 entities. The molecular structures of 5a , 6a and 6d in the solid state were determined by single X‐ray structure analysis. Complexes 5a and 6a are monomers, whereas 6d creates in the solid state a linear open chain coordination polymer by hydrogen bridge formation. Characteristic for 6d is the somewhat distorted trigonal bipyrimidal arrangement around the copper atom with the nBu3P ligands in axial and the C5H3NCO2H oxygen and nitrogen atoms in equatorial positions. In 5a the oxalate connectivity binds in a μ‐1,2,3,4 fashion being part of a planar Cu2(oxalate) core. TG studies of several mono‐ and dicopper dicarboxylates were carried out. Release of the PR3 ligands is recognized and the remaining Cu‐(di)carboxylate unit decomposes to afford elemental copper and CO2. The deposition of copper onto pieces of PVD‐Cu oxidized silicon wafers by applying the spin‐coating process and using 5c and 5d as precursors is discussed. 相似文献
15.
The properties of complexes formed on HZSM-5 and CuZSM-5 zeolites in the course of ammonia and nitromethane adsorption are studied. Ammonia adsorbs on CuZSM-5 and forms two species, which decompose at different temperatures T
dec. One is due to the formation of the Cu2+(NH3)4 complex (T
dec = 450 K), and the other is assigned to ammonia adsorbed on copper(II) compounds, Cu2+O– and Cu2+–O2––Cu2+, or CuO clusters (T
dec = 650–750 K). Ammonia adsorption on Cu+ and Cu0 is negligible compared with that on the Brönsted acid sites and copper(II). Nitromethane adsorbed on HZSM-5 and CuZSM-5 at 400–500 K transforms into a series of products including ammonia. Ammonia also forms complexes with the Brönsted acid sites and copper(II) similar to those formed in the course of adsorption from the gas phase, but the Cu2+(NH3)4 complexes on CuZSM-5 are not observed. Possible structures of ammonia and nitromethane complexes on Brönsted acid sites and the Cu2+ cations in zeolite channels are discussed. The role of these complexes in selective NO
x
reduction by hydrocarbons over the zeolites is considered in connection with their thermal stability. 相似文献
16.
Yan Cheng Shunping Shi Yong Song Bingxin Liu Chunyu Yao Jing Jiang Yong Li Deliang Chen 《International journal of quantum chemistry》2024,124(1):e27289
Density functional theory calculations are performed to analyze the structure and stability of Cu and Cu-K clusters with 3 to 9 atoms. The results indicate that the stability of the clusters decreases after doping with a K atom. With the increase of cluster size, the stability of the clusters shows odd-even alternation. Cu8 and Cu7K clusters exhibit the highest stability. Next, different adsorption sites are considered to investigate the geometry of CunNO and Cun−1KNO clusters. By calculating the adsorption energy and the HOMO-LUMO energy gap, it is determined that both types of reactions are exothermic processes, indicating stable adsorption of NO. Notably, the CunK clusters are more active (stronger adsorption) for NO than the Cun clusters. The most chemically active clusters among CunNO and Cun−1KNO clusters are Cu8NO and Cu7KNO clusters. Finally, electron transfer and Mayer bond order analysis of Cu8NO and Cu7KNO clusters reveal that the N O bond order decreases due to electron transfer when Cu/Cu-K clusters adsorb NO. In this process, the N atom is the electron donor and the Cu atom is the electron acceptor. Fundamental insights obtained in this study can be useful in the design of Cu/Cu-K catalysts. 相似文献
17.
Olatz Larrañaga Dr. Abel de Cózar Prof. Dr. F. Matthias Bickelhaupt Dr. Ronen Zangi Prof. Dr. Fernando P. Cossío 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13761-13773
Density functional theory and Car–Parrinello molecular dynamics simulations have been carried out for model aldol reactions involving aggregates of lithium enolates derived from acetaldehyde and acetone. Formaldehyde and acetone have been used as electrophiles. It is found that the geometries of the enolate aggregates are in general determined by the most favorable arrangements of the point charges within the respective LinOn clusters. The reactivity of the enolates follows the sequence monomer?dimer>tetramer. In lithium aggregates, the initially formed aldol adducts must rearrange to form more stable structures in which the enolate and alkoxide oxygen atoms are within the respective LinOn clusters. Positive cooperative effects, similar to allosteric effects found in several proteins, are found for the successive aldol reactions in aggregates. The corresponding transition structures show in general sofa geometries. 相似文献
18.
The reactions of IMes‐HCl with bimetallic iron‐copper clusters were investigated and it showed that interconversions among bimetallic FexCuy(CO)zn– clusters were induced by IMes‐HCl. The reaction priority of IMes‐HCl with fragments in FexCuy(CO)zn– was also investigated and the reaction behaviors of zero valent Fe(CO)4 and divalent Fe(CO)4 with IMes‐HCl were discussed. 相似文献
19.
Cluster ions ejected from an Li-Mg alloy liquid metal ion source: Observation of MG
2
2+
and MG
3
2+
Yahachi Saito Toshiyuki Ishida Tamotsu Noda 《Journal of the American Society for Mass Spectrometry》1991,2(1):76-80
Ions ejected from a liquid metal ion source of an Li-Mg (10 atom %) alloy have been investigated by using a magnetic mass analyzer. In addition to singly charged homonuclear Li n + (n ≤ 9) and Mg n + (n ≤ 4) and heteronuclear MgmLi n + (m, n ≤ 2) clusters, doubly charged diatomic and triatomic Mg clusters are observed. Discussion is focused on the observability and the formation mechanism of the doubly charged small Mg clusters. A postionization process is suggested for the formation of the doubly charged clusters. 相似文献
20.
Evolution of the metallicity in the Li
n
H
m
clusters as a function of m: evidence for a segregation
R. Antoine Ph. Dugourd D. Rayane E. Benichou B. Vezin M. Broyer 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):436-440
The unimolecular decomposition of metal rich Li n H m + clusters (1 ≤ m ≤ 6, n ≤ 22 and (n ? m) > 3) is studied. The evaporative rates of the mixed clusters display features characteristic of metallic clusters. This confirms and extends to a larger size range the previous results obtained by photoionization and absorption cross section measurements. The evaporative rates are simulated by considering that there is a segregation between a metallic Li n-m + part and an insulating (LiH)m part in the mixed cluster. 相似文献