共查询到20条相似文献,搜索用时 31 毫秒
1.
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. 相似文献
2.
Density functional GGA-PW91 method with DNP basis set is applied to optimize the geometries of Ag
n
H (n = 1–10) clusters. For the lowest energy geometries of Ag
n
H (n = 1–10) clusters, the hydrogen atom prefers to occupy the two-fold coordination bridge site except the occupation of single-fold
coordination site in AgH cluster. After adsorption of hydrogen atom, most Ag
n
structures are slightly perturbed and only the Ag6 structure in Ag6H cluster is distorted obviously. The Ag–Ag bond is strengthened and the strength of Ag–H bond exhibits a clear odd–even oscillation
like the strength of Au–H bond in Au
n
H clusters, indicating that the hydrogen atom is more favorable to be adsorbed by odd-numbered pure silver clusters. The adsorption
strength of small silver cluster toward H atom is obviously weaker than that of small gold cluster toward H atom due to the
strong scalar relativistic effect in small gold cluster. The pronounced odd–even alternation of the magnetic moments is observed
in Ag
n
H systems, indicating that the Ag
n
H clusters possess tunable magnetic properties by adsorbing hydrogen atom onto odd-numbered or even-numbered small silver
cluster. 相似文献
3.
A systematic density functional theory investigation on C2Au
n
+ (n = 1,3,5) and C2Au
n
(n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like Cs C2Au+ (C=C–Au+) and D∞h C2Au2 (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C2v C2Au3
+ ([Au–C≡C–Au]Au+) and Cs C2HAu2
+([H–C≡C–Au]Au+). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au3) in the head-on coordinated C2v C2Au4 (Au–C≡C–Au3) and the side-on coordinated C2v C2Au5
+ ([Au–C≡C–Au]Au3
+). Similar –Au3 triangular units exist in the head-on coordinated C2v C2HAu3 (H–C≡C–Au3) and D2d C2Au6 (Au3–C≡C–Au3). The existence of stable –Au3 triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au3 triangles originates from the fact that an equilateral D3h Au3
+ cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature.
The extension from H/Au analogy to H/Au3 analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials. 相似文献
4.
An all-electron scalar relativistic calculation on Au
n
AgCO (n = 1–12) clusters has been performed using density functional theory with the generalized gradient approximation at PW91 level.
The introduction of impurity silver weakens the adsorption, and, however, promotes the reactivity enhancement of CO molecule.
The CO molecule is relatively more favorable to be adsorbed by the odd-numbered Au
n
Ag clusters with closed-shell electronic structure. The values of chemical hardness indicate that the Au
n
AgCO cluster is less stable than the corresponding Au
n+1CO cluster chemically. This picture of the influence of impurity silver on the adsorption behavior of Au
n
Ag (n = 1–12) clusters toward CO molecule is consistent with previous experimental work (Haeck et al. in J Phys Chem A 115:2103,
2011), in which the cluster’s reaction probability toward CO molecule is reduced upon substitution of gold atoms for silver and
the clusters with closed electronic shell are the most reactive toward CO molecule. 相似文献
5.
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
6.
Serdar Öğüt Juan C. Idrobo Julius Jellinek Jinlan Wang 《Journal of Cluster Science》2006,17(4):609-626
We examine low-energy isomeric forms, static polarizabilities, and optical absorption spectra of Ag
n
, n = 2–8, and Au
n
, n = 2–3, clusters using first principles computations within the static and time-dependent versions of the density functional theory. The noticeable decrease in the static polarizabilities of Ag7 and Ag8 compared to the values characteristic of Ag
n
, n = 2–6, is correlated with the transition from two-dimensional to three-dimensional structures at n = 7. The optical spectra computed within the time-dependent local density approximation for the most stable structures are in good agreement with the available experimental data and the results of earlier theoretical studies. Optical spectra of higher-energy isomers typically present features that are not observed in the experimental spectra. The d electrons affect the spectra of noble metal clusters by quenching the oscillator strengths through screening of the s electrons and by getting directly involved in the excitations. Due to the larger s–d hybridization in Au compared to Ag, these effects are more pronounced in Au
n
clusters. 相似文献
7.
Ahmed A. Mohamed Hanan E. Abdou Andrew Mayer John P. Fackler Jr. 《Journal of Cluster Science》2008,19(4):551-559
Abstract Attempts to remove the halide atoms from [Au2(hpp)2Cl2], 1, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, with Ag(I) benzoate lead to the formation of the Au(I)–Ag(I) product, [(PhCOO)2Au4(hpp)4Ag2(PhCOO)4], 2. This material is stable to air and light at room temperature and shows a UV–vis spectrum in THF with absorbances at 575,
440, 345, and 273 nm. The mixed metal product crystallizes as green crystals in the monoclinic space group P21/n. The Au–Au distances of 2.4473(19) ? are the shortest gold–gold distances reported to date. The gold···silver distance is
3.344(3) ? and the silver···silver distance is 2.771(6) ?. This latter distance is short compared with the Ag···Ag distance
of 2.902(3) ? in the eight-membered silver benzoate dimer starting material. The Au(II) hpp and Ag(I) benzoate components
are linked by carboxylate groups and two gold-silver interactions. This result stands in structural contrast to terminal carboxylate
products observed with Au(II) ylides and amidinates wherein the carboxylate is not bridging to another metal atom.
Index Abstract Three equivalents of silver benzoate react with [Au2(hpp)2Cl2], 1, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, to form the gold(II)-silver(I) product, 2, [(PhCOO)2Au4(hpp)4Ag2(PhCOO)4]. The gold–gold distance of 2.4473(19) ? is the shortest gold–gold distance reported to date. The gold–silver distance is
3.344(3) ? and the silver–silver distance is 2.771(6) ?.
Dedicated to the memory of F. Albert Cotton (1930–2007). 相似文献
8.
Zhi-Wei Zhao Hui-Yan Zhao Jing Wang Qing-Min Ma Ying Liu You-Cheng Li 《Journal of Cluster Science》2012,23(1):133-145
The lowest-energy configurations, electronic structures and magnetic moments of small Lu
n
(n = 2–20) clusters have been investigated within the framework of density functional theory. The results show that Lu
n
(n = 4, 8, 13, and 18) clusters are more stable than their respective neighbors, and structural transformation reveals at n = 16. As the number of atoms increases, the magnetic moments increase in an alternating fashion until they reach a maximum
of 4.00 μB for Lu8 clusters, followed by even–odd oscillation between 0.00 and 1.00 μB over the range n = 9–20. 相似文献
9.
Lang SM Claes P Neukermans S Janssens E 《Journal of the American Society for Mass Spectrometry》2011,22(9):1508-1514
Structural information on free transition metal doped aluminum clusters, Al
n
TM
+ (TM = Ti, V, Cr), was obtained by studying their ability for argon physisorption. Systematic size (n = 5 – 35) and temperature (T = 145 – 300 K) dependent investigations reveal that bare Al
n
+ clusters are inert toward argon, while Al
n
TM
+ clusters attach one argon atom up to a critical cluster size. This size is interpreted as the geometrical transition from
surface-located dopant atoms to endohedrally doped aluminum clusters with the transition metal atom residing in an aluminum
cage. The critical size, n
crit
, is found to be surprisingly large, namely n
crit = 16 and n
crit = 19 – 21 for TM = V, Cr, and TM = Ti, respectively. Experimental cluster–argon bond dissociation energies have been derived as function of cluster size from
equilibrium mass spectra and are in the 0.1–0.3 eV range. 相似文献
10.
The (CH3OH)
n
(n = 2–8) clusters formed via hydrogen bond (H-bonds) interactions have been studied systemically by density functional theory
(DFT). The relevant geometries, energies, and IR characteristics of the intermolecular OH···O H-bonds have been investigated.
The quantum theory of atoms in molecule (QTAIM) and natural bond orbital (NBO) analysis have also been applied to understand
the nature of the hydrogen bonding interactions in clusters. The results show that both the strength of H-bonds and the deformation
are important factors for the stability of (CH3OH)
n
clusters. The weakest H-bond was found in the dimer. The strengths of H-bonds in clusters increase from n = 2 to 8, moreover, the strengths of H-bonds in (CH3OH)
n
(n = 4–8) clusters are remarkably stronger than those in (CH3OH)
n
(n = 2, 3) clusters. The small differences of the strengths of H-bonds among (CH3OH)
n
(n = 6–8) clusters indicate that a partial covalent character is attributed to the H-bonds in these clusters. The linear relationships
between the electron density of BCP (ρb) and the H···O bond length of H-bonds as well as the second-perturbation energies E(2) have also been investigated and used to study the nature of H-bonds, respectively. 相似文献
11.
Density functional study of structural and electronic properties of maximum‐spin n+1Aun−1Ag clusters
Zhen‐Yi Jiang Yu‐Qin Hou Kuo‐Hsing Lee San‐Yan Chu 《International journal of quantum chemistry》2009,109(6):1348-1356
The structures and relative stabilities of high‐spin n+1Aun?1Ag and nAun?1Ag+ (n = 2–8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high‐spin neutral or cationic Aun?1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high‐spin neutral or cationic Aun clusters. The properties of mixed gold–silver clusters are strongly sized and structural dependence. The high‐spin bimetallic clusters tend to be holding three‐dimensional geometry rather than planar form represented in their low‐spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high‐spin clusters, which is different from its position occupied by light atom in the low‐spin situations. Our theoretical calculations indicated that in various high‐spin Aun?1Ag neutral and cationic species, 5Au3Ag, 3AuAg and 5Au4Ag+ hold high stability, which can be explained by valence bond theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
12.
Possible geometrical structures and relative stabilities of (F2AlN3)
n
(n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F2AlN3)
n
(n = 2–4) possess cyclic structure containing Al–Nα–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F2AlN3)
n
(n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm−1, and the vibrational modes are N3 asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters
(2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K. 相似文献
13.
Jia Cao Qi Li Zhi Xiang Wang Lou Jun Gao Feng Fu Bo Fan Yao Wang 《Journal of Cluster Science》2016,27(3):993-1004
The geometric structures, relative stabilities, magnetic properties of Mo-doped gold clusters Au n Mo(n = 1–10) have been investigated at the PBE1PBE/def2TZVP level of theory. The results show that molybdenum doping has a significant effect on the geometric structures and electronic properties of Au n Mo(n = 1–10) clusters. For the lowest energy structures of Au n Mo(n = 1–10), the two dimensional to three dimensional transition occurs at cluster size n ≥ 8, and their relative stabilities exhibit odd–even oscillation with the change of Au atom number. It is found that charge in corresponding Au n Mo clusters transfers from Mo atom to Au n host in the size range n = 1–7, whereas the charge in opposition direction in the size range n = 8–10. In addition, the magnetic properties of Au n Mo clusters are enhanced after doping single Mo atom into the corresponding gold clusters. Our results are valuable for the design of magnetic material. 相似文献
14.
S. N. Lanin D. A. Pichugina A. F. Shestakov V. V. Smirnov S. A. Nikolaev K. S. Lanina A. Yu. Vasil’kov Fam Tien Zung A. V. Beletskaya 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(12):2133-2142
Heats of adsorption Q of n-alkanes C6–C9 on ZrO2 modified with gold and nickel nanoparticles were determined experimentally. The Q values were found to be higher on average by 7 kJ/mol on the modified samples as compared to the pure support. Density functional
theory with the PBE functional and the pseudopotential for gold effectively allowing for relativistic corrections was used
to model the adsorption of saturated hydrocarbons on Au and Au + Ni, as exemplified by the interaction of alkanes C1–C3 with Au
m
, Au
m − 1Ni (m = 3, 4, 5) clusters as well as the interaction of C1–C8 with Au20. Based on the calculation results, the probable coordination centers of alkanes on nanoparticle surfaces were found to be
vertices and edges, whereas face localization was less probable. 相似文献
15.
An all-electron (AE) calculation on the geometrical structures and possible dissociation channels of MnP
n
+ (n = 2–8) cluster ions has been performed by using density functional theory with the generalized gradient approximation (GGA)
at PW91 level. The lowest energy structures of MnP
n
+ (n = 2–8) cluster ions may be regarded as the outcome of bonding between Mn atom and one or two units of P2, P3, and P4. The most possible dissociation channels of MnP
n
+ (n = 2–8) cluster ions are the detachment of P2, P3, or P4 unit. These conclusions are basically consistent well with previous works in which the P2 and P4 structures are regarded as two relatively stable units and easy to be stripped. 相似文献
16.
Geometry optimizations were performed on monoanionic and dianionic clusters of sulfate anions with carbon dioxide, SO4−1/−2(CO2)
n
, for n = 1–4, using the B3PW91 density functional method with the 6-311 + G(3df) basis set. Limited calculations were carried out with the CCSD(T) and MP2 methods. Binding energies, as well as adiabatic
and vertical electron detachment energies, were calculated. No covalent bonding is seen for monoanionic clusters, with O3SO–CO2 bond distances between 2.8 and 3.0 ?. Dianionic clusters show covalent bonding of type [O3S–O–CO2]−2, [O3S–O–C(O)O–CO2]−2, and [O2C–O–S(O2)–O–CO2]−2, where one or two oxygens of SO4−2 are shared with CO2. Starting with n = 2, the dianionic clusters become adiabatically more stable than the corresponding monoanionic ones. Comparison with SO4−1/−2(SO2)
n
and CO3−1/−2(SO2)
n
clusters, the binding energies are smaller for the present SO4−1/−2(CO2)
n
systems, while stabilization of the dianion occurs at n = 2 for both SO4−2(CO2)
n
and SO4−2(SO2)
n
, but only at n = 3 for CO3−2(SO2)
n
. 相似文献
17.
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
18.
Shamoon Ahmad Siddiqui 《Structural chemistry》2012,23(1):267-274
Quantum chemical calculations using gradient corrected density functional theory at B3LYP level reveals the unusual properties
of a chromium (Cr) atom interacting with fluorine (F) atoms. Up to seven F atoms are bound to a single Cr atom, which results
in increase of electron affinities as successive fluorine atoms are attached, reaching a peak value of 7.14 eV for CrF6. The large HOMO–LUMO energy gap, both in neutral and anionic form, further provide evidence of their stability. These unusual
properties brought about by involvement of inner shell 3d-electrons, which not only allow CrF
n
(n = 1–7) clusters to belong to the class of superhalogens but also show that its valence can exceed the nominal value of 2. 相似文献
19.
Prof. Dr. Bo‐Tao Teng Feng‐Min Wu Prof. Dr. Wei‐Xin Huang Dr. Xiao‐Dong Wen Prof. Lei‐Hong Zhao Meng‐Fei Luo 《Chemphyschem》2012,13(5):1261-1271
Studying the structures of metal clusters on oxide supports is challenging due to their various structural possibilities. In the present work, a simple rule in which the number of Au atoms in different layers of Aux clusters is changed successively is used to systematically investigate the structures of Aux (x=1–10) clusters on stoichiometric and partially reduced CeO2(111) surface by DFT calculations. The calculations indicate that the adsorption energy of a single Au atom on the surface, the surface structure, as well as the Au? Au bond strength and arrangement play the key roles in determining Aux structures on CeO2(111). The most stable Au2 and Au3 clusters on CeO2(111) are 2D vertical structures, while the most stable structures of Aux clusters (x>3) are generally 3D structures, except for Au7. The 3D structures of large Aux clusters in which the Au number in the bottom layer does not exceed that in the top layer are not stable. The differences between Aux on CeO2(111) and Mg(100) were also studied. The stabilizing effect of surface oxygen vacancies on Aux cluster structures depends on the size of Aux cluster and the relative positions of Aux cluster and oxygen vacancy. The present work will be helpful in improving the understanding of metal cluster structures on oxide supports. 相似文献
20.
Z. Rzączyńska J. Sienkiewicz-Gromiuk H. Głuchowska 《Journal of Thermal Analysis and Calorimetry》2010,101(1):213-219
Rare earth complexes with 2,2′-biphenyldicarboxylic acid (diphenic acid = H2dpa) were obtained as hydrated precipitates of the general formula Ln2(C14H8O4)3∙nH2O, where n = 3 for the of Y(III) and Ce(III)–Er(III) and n = 6 for La(III), Tm(III), Yb(III) and Lu(III) complexes. On heating in air atmosphere complexes lose all water molecules in the
temperature range 30–210 °C in one step and form anhydrous compounds, which are stable up to 315–370 °C. During further heating
they decompose to oxides. The trihydrated compounds are crystalline powders whereas the hexahydrated are amorphous solids.
The trihydrated complexes crystallize in the monoclinic (Pr(III) and Ce(III) complexes) and triclinic (Y(III) and Nd(III)–Er(III)
complexes) crystal systems. 相似文献