Density functional study of the interaction of chlorine atom with small neutral and charged silver clusters

Chlorine adsorption on small neutral, anionic, and cationic silver clusters Ag(n) (n=2-7) has been studied using the PW91PW91 density functional method. It was found that the adsorption of chlorine on the lowest-energy bare clusters does not always produce the lowest-energy complexes. In addition, the binding of chlorine can greatly change the geometries of the silver clusters in some cases. Among various possible adsorption sites, bridge site is energetically preferred for the neutral Ag(n) while top site is energetically more preferred for the anionic Ag(n) with n< or =6. For cationic clusters, adsorptions on bridge and face sites have similar binding energies, which are much larger than those on top sites. Natural bond orbital analyses show that irrespective of charge state, electrons always transfer from silver atoms to adsorbate and silver acts like alkali metals in the interaction with chlorine atom. Significant odd-even alternation patterns in the properties of the complexes have been observed: Even-electron clusters often have higher ionization energies, lower electron affinities, and higher dissociation energies than their odd-electron neighbors. It was also found that chlorine atoms bind more strongly with odd-electron bare clusters than with even-electron bare clusters. These patterns reveal that even-electron clusters are more stable than odd-electron clusters.     

Density functional study of small neutral and charged silver cluster hydrides

Small neutral, anionic, and cationic silver cluster hydrides AgnH and anionic HAgnH (n=1-7) have been studied using the PW91PW91 density functional method. It was found that the most stable structure of the AgnH complex (neutral or charged) does not always come from that of the lowest energy bare silver cluster plus an attached H atom. Among various possible adsorption sites, the bridge site is energetically preferred for the cationic and most cases of neutral Agn. For anionic Agn, the top site is preferred for smaller Agn within n相似文献   

Density functional study of carbon monoxide adsorption on small cationic,neutral, and anionic aluminum nitride clusters

CO adsorption on small cationic, neutral, and anionic (AlN)_n (n = 1–6) clusters has been investigated using density functional theory in the generalized gradient approximation. Among various possible CO adsorption sites, an N on‐top (onefold coordinated) site is found to be the most favorable one, irrespective of the charge state of the clusters. The adsorption energies of CO on the anionic (AlN)_nCO (n = 2–4) clusters are greater than those on the neutral and cationic complexes. The adsorption energies on the cationic and neutral complexes reflect the odd–even oscillations, and the adsorption energies of CO on the cationic (AlN)_nCO (n = 5, 6) clusters are greater than those on the neutral and anionic complexes. The adsorption energies for the different charge states decrease with increasing cluster size. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Experimental and theoretical study of the reactions between small neutral iron oxide clusters and carbon monoxide

Reactions of small neutral iron oxide clusters (FeO(1-3) and Fe(2)O(4,5)) with carbon monoxide (CO) are investigated by experiments and first-principle calculations. The iron oxide clusters are generated by reaction of laser-ablation-generated iron plasma with O(2) in a supersonic expansion and are reacted with carbon monoxide in a fast flow reactor. Detection of the neutral clusters is through ionization with vacuum UV laser (118 nm) radiation and time-of-flight mass spectrometry. The FeO(2) and FeO(3) neutral clusters are reactive toward CO, whereas Fe(2)O(4), Fe(2)O(5), and possibly FeO are not reactive. A higher reactivity for FeO(2) [sigma(FeO(2) + CO) > 3 x 10(-17) cm(2)] than for FeO(3) [sigma(FeO(3) + CO) approximately 1 x 10(-17) cm(2)] is observed. Density functional theory (DFT) calculations are carried out to interpret the experimental observations and to generate the reaction mechanisms. The reaction pathways with negative or very small overall barriers are identified for CO oxidation by FeO(2) and FeO(3). The lower reactivity of FeO(3) with respect to FeO(2) may be related to a spin inversion process present in the reaction of FeO(3) with CO. Significant reaction barriers are calculated for the reactions of FeO and Fe(2)O(4-5) with CO. The DFT results are in good agreement with experimental observations. Molecular-level reaction mechanisms for CO oxidation by O(2), facilitated by condensed phase iron oxides as catalysts, are suggested.     

Density functional study of small molybdenum clusters

Small molybdenum clusters up to the tetramer are investigated within the framework of the density functional theory. Both the geometry and the spin state are optimized for the dimer, trimer, and the tetramer. Moreover, all those calculations are followed by a vibrational analysis to discriminate between real minima and saddle points on the potential energy surfaces. Several low‐lying excited states are found to be stable after the vibrational analysis. Equilibrium geometries, electronic configurations, binding energies, magnetic moments, and harmonic frequencies of the stable conformers are reported. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 76: 105–112, 2000     

Density functional investigation of the interaction of acetone with small gold clusters

The structural evolution of Au(n) (n=2, 3, 5, 7, 9, and 13) clusters and the adsorption of organic molecules such as acetone, acetaldehyde, and diethyl ketone on these clusters are studied using a density functional method. The detailed study of the adsorption of acetone on the Au(n) clusters reveals two main points. (1) The acetone molecule interacts with one gold atom of the gold clusters via the carbonyl oxygen. (2) This interaction is mediated through back donation mainly from the spd-hybridized orbitals of the interacting gold atom to the oxygen atom of the acetone molecule. In addition, a hydrogen bond is observed between a hydrogen atom of the methyl group and another gold atom (not involved in the bonding with carbonyl oxygen). Interestingly, the authors notice that the geometries of Au(9) and Au(13) undergo a significant flattening due to the adsorption of an acetone molecule. They have also investigated the role of the alkyl chain attached to the carbonyl group in the adsorption process by analyzing the interaction of Au(13) with acetaldehyde and diethyl ketone.     

Far-infrared spectroscopy of small neutral silver clusters

The vibrational spectra of Ag(3) and Ag(4) are recorded in the far-infrared between 100 and 220 cm(-1) using multiple photon dissociation spectroscopy of their complexes with Ar atoms. For Ag(3)-Ar two IR active bands are found at 113 and 183 cm(-1), for Ag(4)-Ar one band at 163 cm(-1) and very weak IR activity at 193 cm(-1) are observed. This, together with recent theoretical studies, allows for a reassignment of the controversial vibrational data reported earlier for the bare Ag(3) cluster. The influence of the number of Ar atoms in the complexes on the frequency of the IR active modes is found to be minor. However, the low-frequency IR-active band of Ag(3) shifts with increasing Ar coverage from 113 cm(-1) for Ag(3)-Ar to about 120 cm(-1) for Ag(3)-Ar(4), the value known for Ag(3) embedded in rare gas matrices.     

Size-dependent carbon monoxide adsorption on neutral gold clusters

We report on experiments probing the reactivity of neutral Au(n) clusters, n = 9-68, with carbon monoxide. The gold clusters are produced in a pulsed laser vaporization cluster source, operated at room temperature (RT) or at liquid-nitrogen temperature (LNT), pass through a low-pressure reaction cell containing CO gas, and are subsequently laser ionized. The reaction probabilities are determined by recording mass abundance spectra with time-of-flight mass spectrometry. The main observations are a strong temperature dependence and a remarkable size dependence. Upon cooling of the cluster source to LNT, the reactivity increases substantially. At LNT, the reaction probabilities for Au(n) with the first CO molecule are about a factor 10 higher than at RT. Moreover, adsorption of two, three, and even four CO molecules is observed, in contrast to RT clusters which at most adsorb one CO molecule. This temperature dependence is related to the lifetime of the cluster-molecule complexes, being much longer for cold clusters. The observed striking size dependence is similar at both temperatures and is discussed in terms of the electronic structure effects.     

Density functional theory study of small vanadium oxide clusters

Density functional theory is employed to study structure and stability of small neutral vanadium oxide clusters in the gas phase. BPW91/LANL2DZ level of theory is used to obtain structures of VOy (y=1-5), V2Oy (y=2-7), V3Oy (y=4-9), and V4Oy (y=7-12) clusters. Enthalpies of growth and fragmentation reactions of the lowest energy isomers of vanadium oxide molecules are also obtained to study the stability of neutral vanadium oxide species under oxygen saturated gas-phase conditions. Our results suggest that cyclic and cage-like structures are preferred for the lowest energy isomers of neutral vanadium oxide clusters, and oxygen-oxygen bonds are present for oxygen-rich clusters. Clusters with an odd number of vanadium atoms tend to have low spin ground states, while clusters with even number of vanadium atoms have a variety of spin multiplicities for their ground electronic state. VO2, V2O5, V3O7, and V4O10 are predicted to be the most stable neutral clusters under the oxygen saturated conditions. These results are in agreement with and complement previous gas-phase experimental studies of neutral vanadium oxide clusters.     

Density functional study of the structural,electronic, and magnetic properties of neutral and charged rhodium clusters up to tetramer

Model core potential computations were performed for Rh₂, Rh₃, and Rh₄ clusters and their respective cations and anions using the linear combination of Gaussian‐type orbital, nonlocal spin density method. The optimized geometries, electronic and magnetic structures, binding and fragmentation energies, adiabatic ionization potentials, and electron affinities were determined. Results show that the ionization potentials, electron affinities, binding energies, and magnetic moments decrease with the cluster size. For Rh₂ and Rh₃ the most stable structures exhibit ferromagnetic properties, while Rh₄ in its ground state is found to be paramagnetic. The structures of minimum energy for the charged species often differs from the corresponding neutral one. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Theoretical study of HCN and HNC neutral and charged clusters

A theoretical study of linear and cyclic clusters of (HCN)n and (HNC)n (up to n = 10) has been carried out by means of DFT and MP2 ab initio methods. The transition states linking the cyclic clusters show high energetic barriers that prevent the spontaneous transformation of the high-energy clusters, (HNC)n, into the low-energy ones, (HCN)n. The effect of the protonation/deprotonation of the linear clusters has also been explored. The results show that (HNC)n clusters with n values larger than six are thermodynamically more stable as charged systems than as neutral ones. The geometrical results have been analyzed using a Steiner-Limbach plot. The electron density and its Laplacian at the bond critical points correlate with the corresponding bond distances by means of two exponential functions, one for the open shell and another for the closed shell cases.     

Quantum chemical study of neutral and single charged palladium clusters

The extended Hückel (EH) method with an electrostatic two-body correction, has been used in order to determine the structures of small single charged Pd_n clusters with n=2–13 and to compare them with the neutral ones. The results for Pd₂ and Pd₃ are compared with density functional (DFT) calculations. Both cation and anion formations were found to strengthen the clusters due to the bonding character of their HOMO and antibonding nature of LUMO. The twin formation with bond lengths significantly smaller than those in the bulk palladium and in the corresponding neutral particles was found to be the preferential way of growth for anionic clusters; cationic clusters show a more complicated behavior. The promotion of occupation of Pd 5s AOs is suggested to be responsible for the formation of 3D structures, whereas the stability of the planar configurations is attributed to the appearance of the vacancy in the valence 4d-shell. As a result of stronger intermetallic interaction in charged clusters, both excess and deficit of electron density were found to cause the significant broadness of the d-zone.     

The interaction of nitrogen and carbon monoxide with certain ions and neutral species

MNDO method is used to study the interaction of nitrogen and carbon monoxide molecules with a proton, hydrogen atom, hydride ion, hydrogen molecule ion and hydrogen molecule. Predicted geometries and heats of reaction of different complexes are presented. The wave functions are analyzed in terms of ground state charge distributions and overlap populations. Electronic effects accompanying complexation are also discussed.     

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.     

Stability of multiply charged silver clusters

Using the gasaggregation technique it is possible to generate metal clusters in narrow size distributions and to vary their mean size by adjusting the cell parameters. The high intensity of this source allows to detect besides singly charged clusters also multiply charged ones. Ag _n ²⁺ and Ag _n ³⁺ are observed forn≧9 andn≧31, respectively; i.e. at values well below the critical sizes reported for spheres.     

Shell correction study of fission of doubly charged silver clusters

Fission of doubly charged silver clusters is investigated by the method of shell corrections. The following fission events are considered: Ag ₂₂ ²⁺ → Ag _n ⁺ + Ag _{22 ?n} ⁺ , (n=11, 10, 9, 8); Ag ₂₁ ²⁺ → Ag _n ⁺ + Ag _{21 ?n} ⁺ , (n=10, 9, 8, 7); Ag ₁₈ ²⁺ → Ag _n ⁺ + Ag _{18 ?n} ⁺ , (n=9, 8, 7, 6). It is found that the shell correction energy is comparable to or larger than the deformation energy of the liquid drop. Threshold energies for the fission events are calculated and compared with the experimental abundance spectra obtained by Katakuse et al. (1990). Correspondence between the calculated threshold energies with the shell corrections and the experimental abundance is very good, showing products from lower threshold fission channels yield more abundance. The threshold energies without the shell corrections are almost constant irrespective of the fission channels and cannot explain the experimental abundance. Abundance of some products are too small to be accounted for only by the threshold energies. The low abundance of those products may be explained by the presence of competing fission channels that have similar minimal energy paths. It is found in fission of Ag ₁₈ ²⁺ that the shell correction overwhelms the Coulomb energy and the fission channel to Ag₈ + Ag ₁₀ ²⁺ is preferred over the fission channel to Ag ₈ ⁺ + Ag ₁₀ ⁺ .     

Density functional theory study of BnC clusters

B_nC clusters (n = 3–10) were studied at the density functional theory (DFT) (B3LYP)/6‐311G** level of theory. The calculations predicted that the most stable configurations of the B_nC clusters are the (n + 1)‐membered cyclic structures. For boron–carbon clusters, the configurations containing greater numbers of three‐membered boron rings are more favorable, except for the B₇C and B₉C clusters. Through molecular orbital analysis of these B_nC clusters, we have concluded that π‐electron delocalization plays a crucial role in the stability of n + 1‐membered cyclic structures. In this paper, the relative stability of each cluster is discussed based on their single atomic‐binding energies. The capability of clusters to obtain or lose an electron was also discussed, based on their vertical electron detachment energies (VDEs), adiabatic electron detachment energies (ADEs), vertical electron affinities (VEAs) and adiabatic electron affinities (AEAs). Copyright © 2011 John Wiley & Sons, Ltd.     

Density functional study of tetrahedral manganese clusters

We have applied the ab initio density functional theory (DFT) based on generalized spin orbital (GSO) for tetrahedral manganese clusters with a noncollinear spin structure. It was found that three-dimensional (3D) spin states become clearly ground-states by all of GSO-localized spin density approximation, GSO-generalized gradient approximation, and GSO-hybrid methods for tetrahedral Mn(II)₄O₄. These results are consistent with the experimental results.     

Density functional study of AgnPd and AgnPdH clusters

Small Ag_nPd (n = 5) clusters and their hydrides Ag_nPdH (n = 5) have been studied by density functional theory calculations. For bare clusters, the structures in which the Pd atom has a maximum number of neighboring Ag atoms tend to be energetically favorable. Hydrogen prefers binding to Ag? Pd bridge site of Ag_nPd clusters except for Ag₅Pd. The binding energy has a strong odd–even oscillation. The electron transfers are from Ag atoms to Pd in bare clusters and are from metal clusters to H in cluster hydrides. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011