Reactions of Al(n)I(x)- with methyl iodide: the enhanced stability of Al7I and the chemical significance of active centers

Al(n)I(x)- are reacted with methyl iodide, and the reaction mechanisms and products are discussed. The relevance of previous studies of the reactions between bare aluminum clusters and methyl iodide is addressed, and the chemical differences reported herein are explained. Particular attention is given to parallels with the known chemistry of alkyl halides on aluminum surfaces, where kinetically mediated etching reactions are prominent. The emergence of Al7I- as the dominant product in the present reactions is addressed via electronic structure calculations, which reveal that the cluster can be described in terms of an electron bound to a "jellium compound". Other significant products of the etching reaction include I-, I3-, and, importantly, the polyhalide-like Al13I2x- clusters. In the Al13I(x)- series, clusters with odd values for x are found to be reactive, and those with even x are far more stable. This observation is explained in terms of the presence or absence of active sites.     

Structures and electronic properties of Al7x0,- and Al13 X1,2,12- clusters with X=F, Cl, and Br

The structures, binding energies, and electronic properties for Al7X, Al7X-, Al13X-, Al13X2-, and Al13X12- (X = F, Cl, Br) were studied at the B3LYP/6-311+G(2d,p) level. Among the systems studied, Al7 and Al13 clusters in Al7X and Al13X- reveal alkali-like and halogen-like superatom characters, respectively. Al7 can bind with one halogen atom to form a salt-like compound as Al7+delta-X-delta. Al13- can combine with one halogen atom to form a diatomic halogen anion Al13X-. However, when adding more halogens, the superatom structure would be destroyed, resulting in low-symmetry compounds with the center Al atom moving toward the cluster surface. The structures of Al13X1,2,12- (X = F, Cl, Br) are similar to those of X = I; however, their binding energies and electron structures are much different. In addition, the analyses of the calculated NBO charges show that Cl and Br have similar properties, but much different from F, when interacting with the Al clusters. The Al-Cl and Al-Br bonds have more covalent character in Al7X and Al13X2,12-, in contrast to the corresponding Al-F bond, which has prominent ionic character.     

Does the Al13- core exist in the Al13 polyhalide Al13I(n)- (n = 1-12) clusters?

We have studied the structures and stabilities of Al(13)I(n) (-)(n = 1-12) clusters at the density-functional level of theory. Unlike the case of Al(13)I(-), the Al(13)I(n) (-)(n=2-12) clusters do not have an Al(13) (-) core electronically. Population analysis shows that a significant charge transfer occurs from the Al cluster to the I atoms, where the populations for Al(13) vary from -0.48(Al(13)I(2) (-)) to +0.97(Al(13)I(12) (-)). Moreover, the shape of Al(13) moieties in the Al(13)I(n) (-) (n > or = 6 or 7) clusters is significantly distorted from the structure of Al(13) (-), an icosahedron, and is a "cagelike" form, which can be explained by both electronic and steric reasons. Our theoretical results are in good agreement with the experimental observations of Bergeron et al. [Science 307, 231 (2005)].     

Microhydration of X2 gas (X = Cl, Br, and I): a theoretical study on X2.nH2O clusters (n = 1-8)

Structure and properties of hydrated clusters of halogen gas, X2.nH2O (X = Cl, Br, and I; n = 1-8) are presented following first principle based electronic structure theory, namely, BHHLYP density functional and second-order Moller-Plesset perturbation (MP2) methods. Several geometrical arrangements are considered as initial guess structures to look for the minimum energy equilibrium structures by applying the 6-311++G(d,p) set of the basis function. Results on X2-water clusters (X = Br and I) suggest that X2 exists as a charge separated ion pair, X+delta-X-delta in the hydrated clusters, X2.nH2O (n > or = 2). Though the optimized structures of Cl2.nH2O clusters look like X2.nH2O (X = Br and I) clusters, Cl2 does not exist as a charge separated ion pair in the presence of solvent water molecules. The calculated interaction energy between X2 and solvent water cluster increases from Cl2.nH2O to I2.nH2O clusters, suggesting solubility of gas-phase I2 in water to be a maximum among these three systems. Static and dynamic polarizabilities of hydrated X2 clusters, X2.nH2O, are calculated and observed to vary linearly with the size (n) of these water clusters with correlation coefficient >0.999. This suggests that the polarizability of the larger size hydrated clusters can be reliably predicted. Static and dynamic polarizabilities of these hydrated clusters grow exponentially with the frequency of an external applied field for a particular size (n) of hydrated cluster.     

Reactivity of molecular oxygen with aluminum clusters: Density functional and Ab Initio molecular dynamics simulation study

Dissociative adsorption of molecular oxygen (O₂) on aluminum (Al) clusters has attracted much interest in the field of surface science and catalysis, but theoretical predictions of the reactivity of this reaction in terms of barrier height is still challenging. In this regard, we systematically investigate the reactivity of O₂ with Al clusters using density functional theory (DFT) and atom‐centered density matrix propagation (ADMP) simulations. We also calculate potential energy surfaces (PESs) of the reaction between O₂ and Al clusters to estimate the barrier energy of this reaction. The M06‐2X functional gives the barrier energy in agreement with the one calculated by coupled cluster singles and doubles with perturbed triples (CCSD(T)) while the TPSSh functional significantly underestimates the barrier height. The ADMP simulation using the M06‐2X functional predicts the reactivity of O₂ with the Al cluster in agreement with the experimental findings, that is, singlet O₂ readily reacts with Al clusters but triplet O₂ is less reactive. We found that the ability of a DFT functional to describe the charge transfer appropriately is critical for calculating the barrier energy and the reactivity of the reaction of O₂ with Al clusters. The M06‐2X functional is relevant for investigating chemical reactions involving Al and O₂. © 2016 Wiley Periodicals, Inc.     

Gas-phase lanthanide chloride clusters: relationships among ESI abundances and DFT structures and energetics

Anionic lanthanide chloride clusters, Ln(n)Cl(3n+1)(-), were produced by electrospray ionization (ESI) of LnCl(3) in isopropanol, where Ln = La-Lu (except Pm); the clusters were characterized using a quadrupole ion trap mass spectrometer. High-abundance "magic number" clusters were apparent at n = 4 for the early Ln (La-Sm), and at n = 5 for the late Ln (Dy-Lu). Density functional theory computations of La(n)Cl(3n+1)(-) and Lu(n)Cl(3n+1)(-) clusters (n = 1-6) indicate that the clusters with n = 4-6 are rings with a central chlorine atom. Computed structures show six-coordinate Ln in distorted octahedral sites in "magic number" La(4)Cl(13)(-) and Lu(5)Cl(16)(-), which have particularly large dissociation energies. For lanthanum, larger anionic chloride clusters with multiple charges of down to -5 were observed; their fragmentation by collision-induced dissociation in the ion trap revealed La(4)Cl(13)(-) as a common product. Gas-phase hydrolysis to Ln(n)Cl(3n+1-y)(OH)(y)(-) (y = 1, 2) was prevalent for the late lanthanides, but only for small clusters, n = 2 or 3; larger clusters were evidently resistant to gas-phase hydrolysis. ESI of selected LnBr(3) and LnI(3) resulted in Ln(n)X(3n+1)(-) clusters (X = Br, I)--in contrast to Ln(n)Cl(3n+1)(-) clusters, the only observed (minor) high-abundance clusters were La(4)Br(13)(-) and Ce(4)Br(13)(-).     

Structure and stability of the Al14 halides Al14In - (n=1-11): can we regard the Al14 core as an alkaline earthlike superatom?

We have studied the structures and stabilities of Al(14)I(n) (-) (n=1-11) clusters at the density functional level of theory. The experimentally observed Al(14)I(n) (-) (n=3, 5, 7, 9, and 11) [Bergeron et al., Science 307, 231 (2005)] are found to be stable both kinetically and thermodynamically. Al(14)I(3) (-), not Al(14)I(-), is the first member of the Al(14)I(n) (-) series in the mass spectrometric experiment, which is ascribable to the low kinetic stability of the Al(14)I(-) cluster. The Al(14) core in Al(14)I(3) (-) is close to neutral Al(14), both electronically and structurally. Population analysis shows that charge transfer occurs from the Al cluster to the I atoms, where the populations for Al(14) vary from -0.70(Al(14)I(-)) to +0.96(Al(14)I(11) (-)). The Al(14)I(5) (-) and Al(14)I(7) (-) clusters have the structure of Al(14)I(3) (-) as a core framework, but, for n=9 and 11, we found many more stable isomers than the isomers having the Al(14)I(3) (-) core. In particular, the shape of Al(14) in the Al(14)I(11) (-) cluster is a hexagonal wheel-shaped form, which was observed in the x-ray experiment for the metalloid complex [Al(14){N(SiMe(3))(2)}(6)I(6)Li(OEt(2))(2)](-)[Li(OEt(2))(4)](+)toluene [Kohnlein et al., Angew. Chem., Int. Ed. 39, 799 (2000)]. We have demonstrated that a simple jellium model cannot describe the structure and stability of the iodine-doped aluminum clusters, although it is successful for describing those of aluminum clusters. The electronic and geometric changes of the Al(14) (-) cluster due to the presence of iodines are very similar to the case of a magic cluster Al(13) (-). It can be concluded from our electronic and structural analysis that one cannot regard the Al(14) core as an alkaline earthlike superatom in the Al(14) iodide clusters.     

Structural, electronic, and chemical properties of multiply iodized aluminum clusters

The electronic structure, stability, and reactivity of iodized aluminum clusters, which have been investigated via reactivity studies, are examined by first-principles gradient corrected density functional calculations. The observed behavior of Al13I(x)- and Al14I(x)- clusters is shown to indicate that for x < or = 8, they consist of compact Al13- and Al14++ cores, respectively, demonstrating that they behave as halogen- or alkaline earth-like superatoms. For x > 8, the Al cores assume a cagelike structure associated with the charging of the cores. The observed mass spectra of the reacted clusters reveal that Al13I(x)- species are more stable for even x while Al14I(x)- exhibit enhanced stability for odd x(x > or = 3). It is shown that these observations are linked to the formation and filling of "active sites," demonstrating a novel chemistry of superatoms.     

Simulated annealing and density functional theory calculations of structural and energetic properties of the ammonium chloride clusters (NH4Cl)n, (NH4+)(NH4Cl)n, and (Cl-)(NH4Cl)n, n = 1-13

Simulated annealing Monte Carlo conformer searches using the "mag-walking" algorithm are employed to locate the global minima of molecular clusters of ammonium chloride of the types (NH(4)Cl)(n), (NH(4)(+))(NH(4)Cl)(n), and (Cl(-))(NH(4)Cl)(n) with n = 1-13. The M06-2X density functional theory method is used to refine and predict the structures, energies, and thermodynamic properties of the neutral, cation, and anion clusters. For selected small clusters, the resulting structures are compared to those obtained from a variety of models and basis sets, including RI-MP2 and B3LYP calculations. M06-2X calculations predict enhanced stability of the (NH(4)(+))(NH(4)Cl)(n) clusters when n = 3, 6, 8, and 13. This prediction corresponds favorably to anomalies previously observed in thermospray mass spectroscopy experiments. The (NH(4)Cl)(n) clusters show alternations in stability between even and odd values of n. Clusters of the type (Cl(-))(NH(4)Cl)(n) display a magic number distribution different from that of the cation clusters, with enhanced stability predicted for n = 2, 6, and 11. None of the observed cluster structures resemble the room-temperature CsCl structure of NH(4)Cl(s), which is consistent with previous work. Numerous clusters have structures reminiscent of the higher-temperature, rock-salt phase of the solid ammonium halides.     

Finite size effects on aluminum/Teflon reaction channels under combustive environment: a Rice-Ramsperger-Kassel-Marcus and transition state theory study of fluorination

The effect of particle size on combustion efficiency is an important factor in combustion research. Gas-phase aluminum clusters in oxidizing environment constitute a relatively simple and extensively studied system. In an attempt to underscore the correlation between electronic structure, finite size effect, and reactivity in small aluminum clusters, reactions between aluminum, [Al(13)](-) cluster, and Teflon decomposition fragments were studied using theoretical calculations at the density functional theoretical level. The unimolecular rate constants calculated using transition state and Rice-Ramsperger-Kassel-Marcus theory show that reactions with COF and CF(2) species with aluminum are faster than those involving CF(3) and COF(2). The results show that the kinetic barriers along different exothermic reaction channels correlate with the trends in HOMO(R)-HOMO(TS) (HOMO denotes highest occupied molecular orbital) energy gap and related shifts of the HOMO levels of reactants. Overall reactions involving carbonyl fluoride species (COF and COF(2)) lead to CO elimination and fluorination of the Al cluster. The CF(3)/CF(2) fragments lead to stable multicenter Al-C bond formation on the fluorinated Al cluster surface. Temperature-, energy-, and pressure-dependent rate constants are provided for extrapolating the expected reaction kinetics to conditions similar to known combustion reactions.     

Theoretical study of Al(n) and Al(n)O (n = 2-10) clusters

The stable structures, energies, and electronic properties of neutral, cationic, and anionic clusters of Al(n) (n = 2-10) are studied systematically at the B3LYP/6-311G(2d) level. We find that our optimized structures of Al5(+), Al9(+), Al9(-), Al10, Al10(+), and Al10(-) clusters are more stable than the corresponding ones proposed in previous literature reports. For the studied neutral aluminum clusters, our results show that the stability has an odd/even alternation phenomenon. We also find that the Al3, Al7, Al7(+), and Al7(-) structures are more stable than their neighbors according to their binding energies. For Al7(+) with a special stability, the nucleus-independent chemical shifts and resonance energies are calculated to evaluate its aromaticity. In addition, we present results on hardness, ionization potential, and electron detachment energy. On the basis of the stable structures of the neutral Al(n) (n = 2-10) clusters, the Al(n)O (n = 2-10) clusters are further investigated at the B3LYP/6-311G(2d), and the lowest-energy structures are searched. The structures show that oxygen tends to either be absorbed at the surface of the aluminum clusters or be inserted between Al atoms to form an Al(n-1)OAl motif, of which the Al(n-1) part retains the stable structure of pure aluminum clusters.     

Reaction mechanisms of dissociative chemisorption of HI, I2, and CH3I on a magic cluster Al13-

We have investigated the transition-state structures and reaction mechanisms for the dissociative chemisorption reactions of HI, I(2), and CH(3)I on the magic cluster Al(-) (13). The HI, I(2), and CH(3)I molecules approach Al(-) (13) with an end-on orientation rather than a side-on orientation because of the more effective orbital overlap in the end-on orientation. The reactions of Al(-) (13) with HI and I(2) would produce Al(13)HI(-) and Al(13)I(2) (-), respectively, because of large exothermic energy changes and relatively small activation energies. The reaction of Al(-) (13) with CH(3)I is unlikely to take place because of the low mobility of CH(3) on Al(-) (13) and the high activation barrier for the S(N)2-type reaction. The dissociative chemisorption reactions are preferred thermodynamically to the abstractive chemisorption reactions.     

Collision-induced gas-phase reactions of perhalogenated closo-dodecaborate clusters--a comparative study

The gas phase reactivity of perhalogenated closo-dodecaborate clusters [B(12)X(12)](2-) (X = F, Cl, Br, I) with N-tetraalkylated ammonium counter ions was investigated by electrospray ionization ion trap mass spectrometry (ESI-IT-MS). Collisions with the background gases introduced a broad variety of gas phase reactions. This study represents the first experimental approach to a new class of boron-rich boron clusters that are not accessible in the condensed phase. The anionic ion pair [B(12)X(12) + N(C(n)H(2n+1))(4)](-) is generally found as the ion of highest mass. Its reaction sequence starts with an alkyl transfer from the ammonium ion to the dodecaborate cluster. Subsequently, the alkylated intermediate [B(12)X(12) + C(n)H(2n+1)](-) decomposes to give very reactive ions of the general formula [B(12)X(11)](-). These ions possess a free boron vertex and immediately bind to the residual gases N(2) and H(2)O in the ion trap by formation of the corresponding adducts [B(12)X(11) + N(2)](-) and [B(12)X(11) + H(2)O](-). Subsequent fragmentations of the water adduct repetitively substitute halogen atoms by hydroxyl groups. The fragmentation process of the free anion [B(12)X(12)](2-) depends on the applied excitation energy and on the halogen substituent X. A radical dehalogenation of the B(12) unit is observed for X = I, whereas for X = Cl or F the loss of small molecules (mainly BX(3)) dominates. The different reaction behavior is explained by the different electron affinity of the halogens and the strength of the boron-halogen-bonds. Surprisingly, isolation of the fragment ion [B(12)I(9)](-) in the ion trap yields the highly stable [B(24)I(18)](2-) dianion. This observation suggests a reaction between two negative ions in the gas phase.     

Hydrogen dissociation on small aluminum clusters

Transition states and reaction paths for a hydrogen molecule dissociating on small aluminum clusters have been calculated using density functional theory. The two lowest spin states have been taken into account for all the Al(n) clusters considered, with n=2-6. The aluminum dimer, which shows a (3)Π(u) electronic ground state, has also been studied at the coupled cluster and configuration interaction level for comparison and to check the accuracy of single determinant calculations in this special case, where two degenerate configurations should be taken into account. The calculated reaction barriers give an explanation of the experimentally observed reactivity of hydrogen on Al clusters of different size [Cox et al., J. Chem. Phys. 84, 4651 (1986)] and reproduce the high observed reactivity of the Al(6) cluster. The electronic structure of the Al(n)-H(2) systems was also systematically investigated in order to determine the role played by interactions of specific molecular orbitals for different nuclear arrangements. Singlet Al(n) clusters (with n even) exhibit the lowest barriers to H(2) dissociation because their highest doubly occupied molecular orbitals allow for a more favorable interaction with the antibonding σ(u) molecular orbital of H(2).     

Fascinating transformations of donor-acceptor complexes of group 13 metal (Al,Ga, In) derivatives with nitriles and isonitriles: from monomeric cyanides to rings and cages

Formation of the donor-acceptor complexes of group 13 metal derivatives with nitriles and isonitriles X(3)M-D (M = Al,Ga,In; X = H,Cl,CH(3); D = RCN, RNC; R = H,CH(3)) and their subsequent reactions have been theoretically studied at the B3LYP/pVDZ level of theory. Although complexation with MX(3) stabilizes the isocyanide due to the stronger M-C donor-acceptor bond, this stabilization (20 kJ mol(-1) at most) is not sufficient to make the isocyanide form more favorable. Relationships between the dissociation enthalpy DeltaH degrees (298)(diss), charge-transfer q(CT), donor-acceptor bond energy E(DA), and the shift of the vibrational stretching mode of the CN group upon coordination Deltaomega(CN) have been examined. For a given metal center, there is a good correlation between the energy of the donor-acceptor bond and the degree of a charge transfer. Prediction of the DeltaH degrees (298)(diss) on the basis of the shift of CN stretching mode is possible within limited series of cyanide complexes (for the fixed M,R); in contrast, complexes of the isocyanides exhibit very poor Deltaomega(CN) - DeltaH degrees (298)(diss) correlation. Subsequent X ligand transfer and RX elimination reactions yielding monomeric (including donor-acceptor stabilized) and variety of oligomeric cage and ring compounds with [MN]n, [MC]n, [MNC]n cores have been considered and corresponding to thermodynamic characteristics have been obtained for the first time. Monomeric aluminum isocyanides X(2)AlNC are more stable compared to Al-C bonded isomers; for gallium and indium situation is reversed, in qualitative agreement with Pearson's HSAB concept. Substitution of X by CN in MX(3) increases the dissociation enthalpy of the MX(2)CN-NH(3) complex compared to that for MX(3)-NH(3), irrespective of the substituent X. Mechanisms of the initial reaction of the X transfer have been studied for the case X = R = H. The process of hydrogen transfer from the metal to the carbon atom in H(3)M-CNH is thermodynamically favorable and is likely to be intramolecular. By contrast, intramolecular hydrogen transfer in H(3)M-NCH has been definitely ruled out. Head-to-tail dimeric species [H(3)M-(NC)H](2) are formed exothermically and exhibit low H.H distances, which can assist in hydrogen transfer, and are likely to be the starting point for H(2) elimination. Elimination of H(2), CH(4), and C(2)H(6) from X(3)M-(NC)R adducts is very favorable thermodynamically; by contrast, elimination of HCl and CH(3)Cl is highly unfavorable even if formation of oligomer species takes place. Thus, high-temperature generation of gas-phase rings and clusters has been predicted viable in the cases X = H,CH(3) and their presence in the reactor media should not be neglected. Moderate stability of [HMCH(2)NH](4) clusters (especially in the cases M = Ga, In) makes these species viable intermediates of gas-phase reactions. Their formation may be responsible for the carbon contamination in the course of metal organic chemical vapor deposition processes of group 13 binary nitrides.     

The First Mixed-Halide Zirconium Cluster Compounds: Zr(6)Cl(1.6)I(10.4)Be, Zr(6)Cl(1.3)I(10.7)B, and Zr(6)Cl(11.5)I(1.5)B. Matrix Effects and Halogen Substitution in Compact Network Structures

Investigations of the effect of halogen size on structure stability have been conducted in well-reduced and heavily interbridged zirconium chloride-iodide cluster systems. The title compounds are obtained in good yields from reactions of Zr, ZrCl(4), ZrI(4), and B or Be in sealed Ta tubes for approximately 4 weeks at 850 degrees C. Single-crystal diffraction at room temperature established these as Zr(6)Cl(1.65(4))I(10.35(4))Be and Zr(6)Cl(1.27(3))I(10.73(3))B [R&thremacr;, Z = 3, a = 14.3508(8), 14.389(1) ?, c = 9.8777(9), 9.915(2) ?, respectively] and Zr(6)Cl(11.47(2))I(1.53(2))B [P4(2)/mnm, Z = 2, a = 12.030(1) ?, c = 7.4991(8) ?]. These are derivatives of the Zr(6)I(12)C and orthorhombic Zr(6)Cl(13)B structures, respectively, the latter containing unusual linear chains of clusters interbridged by Cl(i-i) that are in turn interconnected by three-bonded Cl(a-a-a) atoms. The random substitution of fractional Cl at specific I sites in the first two, and I for certain Cl in the third, was positionally resolved in all cases. The replacement always occurs at two-bonded X(i), so that single types of halogen are left in sites that interconnect clusters and generate the three-dimensional array. Structural changes seen in both structures are specifically related to relief of X.X crowding in the parent structure (matrix effects). Substitution of Cl for I(i) in the Zr(6)I(12)C type greatly reduces intercluster I.I repulsions and allows, among other things, a 0.20 ? (5.8%) reduction in Zr-I(a-i) intercluster bond lengths. Increased Cl.I repulsions caused by I substitution in orthorhombic Zr(6)Cl(13)B (Pnnm) convert the twisted chains and angular Cl(a-a-a) interchain bridges to planarity in tetragonal Zr(6)Cl(11.5)I(1.5)B. Phase widths found are 0 相似文献   

Nitric oxide decomposition on small rhodium clusters, Rh(n)+/-

The decomposition of nitric oxide on small charged rhodium clusters Rh(n)(+/-) (6 < n < 30) has been investigated by Fourier transform ion cyclotron resonance mass spectrometry. For both cationic and anionic naked clusters, the rates of reaction with NO increase smoothly with cluster size in the range studied without the dramatic size-dependent fluctuations often associated with the reactions of transition-metal clusters. The cationic clusters react significantly faster than the anions and both exhibit rate constants exceeding collision rates calculated by average dipole orientation theory. Both the approximate magnitude and the trends in reactivity are modeled well by the surface charge capture model recently proposed by Kummerl?we and Beyer. All clusters studied here exhibit pseudo-first-order kinetics with no sign of biexponential kinetics often interpreted as evidence for multiple isomeric structures. Experiments involving prolonged exposure to NO have revealed interesting size-dependent trends in the mechanism and efficiency of NO decomposition: For most small clusters (n < 17), once two NO molecules are coadsorbed on a cluster, N(2) is evolved, generating the corresponding dioxide cluster. By analogy with experiments on extended surfaces, this observation is interpreted in terms of the dissociative adsorption of NO in the early stages of reaction, generating N atoms that are mobile on the surface of the cluster. For clusters where n < 13, this chemistry, which occurs independently of the cluster charge, repeats until a size-dependent, limiting oxygen coverage is achieved. Following this, NO is observed to adsorb on the oxide cluster without further N(2) evolution. For n = 14-16 no single end-point is observed and reaction products are based on a small range of oxide structures. By contrast, no evidence for N(2) production is observed for clusters n = 13 and n > 16, for which simple sequential NO adsorption dominates the chemistry. Interestingly, there is no evidence for the production of N(2)O or NO(2) on any of the clusters studied. A simple general mechanism is proposed that accounts for all observations. The detailed decomposition mechanisms for each cluster exhibit size (and, by implication, structure) dependent features with Rh(13)(+/-) particularly anomalous by comparison with neighboring clusters.     

Structures and Electronic Properties of Ni–Al Alloy Clusters from First-Principles Calculations

Using the density functional theory calculations with the PBE exchange–correlation energy functional, we have studied the low-energy structures and electronic properties of Ni–Al alloy clusters for adsorbing or doping an aluminum atom to Ni_n (n = 13, 19, 23, 26, 29 and 55) clusters. The most stable structures of Ni_nAl are viewed as adding an Al atom at the hollow triangle and rhombus site of the icosahedron (n = 13, 55) and double-icosahedron (n = 19, 23, 26 and 29) structures, respectively. For Ni_n?1Al, it can be seen that an Al atom gradually moves from surface (n = 13, 19, 23 and 26) to the interior site (n = 29, 55) in the most stable structures. The electronic properties of the Ni–Al alloy clusters including binding energies, magnetic properties, charge transfer and density of states have also been studied.     

Planar nitrogen-doped aluminum clusters AlxN- (x=3-5)

The electronic and geometrical structures of three nitrogen-doped aluminum clusters, Al(x)N(-) (x=3-5), are investigated using photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra have been obtained for the nitrogen-doped aluminum clusters at four photon energies (532, 355, 266, and 193 nm). Global minimum structure searches for Al(x)N(-) (x=3-5) and their corresponding neutrals are performed using several theoretical methods. Vertical electron detachment energies are calculated using three different methods for the lowest energy structures and low-lying isomers are compared with the experimental observations. Planar structures have been established for all the three Al(x)N(-) (x=3-5) anions from the joint experimental and theoretical studies. For Al(5)N(-), a low-lying nonplanar isomer is also found to contribute to the experimental spectra, signifying the onset of two-dimensional to three-dimensional transition in nitrogen-doped aluminum clusters. The chemical bonding in all the planar clusters has been elucidated on the basis of molecular orbital and natural bond analyses.     

Structure and stability of Al13I clusters

We have performed density functional calculations for the structures and stabilities of Al(13)I at the scalar relativistic pseudopotential and all-electron levels of theory. The Al(13) moiety in Al(13)I is significantly distorted and structurally similar to an Al(13) cation, where the natural population is -0.27e for the I atom. Unlike other Al(13)-M (M=H, alkali metals, and coinage metals) clusters, a C(s)-ontop structure was found to be the most stable form. The Al(13)I cluster has a large Al(13)-I binding energy of 3.11 eV and is more stable, as charge transfer to the electronegative I atom is larger.