Oxygen adsorption at anionic free and supported Au clusters

A review on the use of DFT for the prediction of the properties of nanomaterials

Nanostructured materials have gained immense attraction because of their extraordinary properties compared to the bulk materials to be used in a plethora of applications in myriad fields. In this review article, we have discussed how the Density Functional Theory (DFT) calculation can be used to explain some of the properties of nanomaterials. With some specific examples here, it has been shown that how closely the different properties of nanomaterials (such as optical, optoelectronics, catalytic and magnetic) predicted by DFT calculations match well with the experimentally determined values. Some examples were discussed in detail to inspire the experimental scientists to conduct DFT-based calculations along with the experiments to derive a better understanding of the experimentally obtained results as well as to predict the properties of the nanomaterial. We have pointed out the challenges associated with DFT, and potential future perspectives of this new exciting field.

Probing the structural, electronic, and adsorptive properties of Au16O2- clusters

Great progress has been made in O₂ adsorption on gold clusters. However, systematic investigations of O₂ adsorption on [Formula: see text] clusters have not been reported. Here, we present a systematic study of the structural, electronic, and adsorptive properties of [Formula: see text] clusters by density functional theory (DFT) calculations coupled with stochastic kicking method. Global minimum searches for [Formula: see text] reveal that exohedral derivatives are more favored. Furthermore, the obtained ground-state structure exhibits significant stability, as judged by its larger adsorption energy (1.16 eV) and a larger HOMO-LUMO gap (0.57 eV). The simulated photoelectron spectra (PES) of [Formula: see text] isomers will be instructive to identify the structures in future experiments. There are three interesting discoveries in the present paper: (1) O₂ undergoes chemical adsorption onto the parent [Formula: see text] clusters, but the amount of the adsorption energy is related to the parent [Formula: see text] clusters; (2) the process that O₂ undergoes dissociative adsorption onto the parent [Formula: see text] clusters is exothermic; (3) [Formula: see text] isomers show smaller X-A energy gaps than those of parent [Formula: see text] clusters, reflecting that their geometric and electronic structures are distorted remarkably due to dissociative adsorption of O₂.

Towards Atomically Precise Supported Catalysts from Monolayer-Protected Clusters: The Critical Role of the Support

Controlling the size and uniformity of metal clusters with atomic precision is essential for fine-tuning their catalytic properties, however for clusters deposited on supports, such control is challenging. Here, by combining X-ray absorption spectroscopy and density functional theory calculations, it is shown that supports play a crucial role in the evolution of monolayer-protected clusters into catalysts. Based on the acidic nature of the support, cluster-support interactions lead either to fragmentation of the cluster into isolated Au-ligand species or ligand-free metallic Au⁰ clusters. On Lewis acidic supports that bind metals strongly, the latter transformation occurs while preserving the original size of the metal cluster, as demonstrated for various Au_n sizes. These findings underline the role of the support in the design of supported catalysts and represent an important step toward the synthesis of atomically precise supported nanomaterials with tailored physico-chemical properties.

Remarkable Structural Effect on the Gold-Hydrogen Analogy in Hydrogen-Doped Gold Cluster

In accordance with the well established gold-hydrogen analogy, a hydrogen atom mimics the properties of a gold atom in gold clusters. In a recent study it has been demonstrated that the properties of a hydrogen atom doped small gold cluster (Au₇H) are not in conformity with the aforementioned analogy. In this paper we study the properties of the Au₇H cluster exhaustively to re-examine the validity of the gold-hydrogen analogy in the context of adsorption of CO and O₂ molecules on pristine gold and hydrogen atom doped gold clusters. For this purpose we first determine the most stable structure of the Au₇H cluster by using an ab initio density functional theory based method with generalized gradient approximation (GGA) and Meta-GGA exchange-correlation functionals. We carry out geometry optimization by considering various planar and three-dimensional isomers of the Au₇H cluster as initial geometries. We find that the lowest energy structure of Au₇H is a planar one with C_{2 v} symmetry, and it is very close to the structure of the Au₈ cluster with D_{4 h} symmetry. Furthermore, to examine the validity of the gold-hydrogen analogy we carry out a detailed investigation of the adsorption of CO and O₂ molecules on the most stable as well as various other low energy isomers of the Au₇H cluster. We find that the adsorption energies and the extent of activation of CO and O₂ molecules on the most stable planar isomer of Au₇H are almost the same as those on the parent Au₈ cluster with D_{4 h} symmetry proving the validity of the gold-hydrogen analogy. On the other hand, for the high energy three-dimensional isomers of the Au₇H cluster obtained from the pristine Au₈ cluster with T _d symmetry, we find a significant enhancement in adsorption energy as well as the extent of activation of CO and O₂ molecules as compared to those for the corresponding pristine cluster. Therefore, the high reactivity of the 3D isomer of the Au₇H cluster may be attributed to its existence in a state which is higher in energy than its most stable planar isomer.

First-Principle Investigations of the Interaction between CO and O2 with Group 11 Atoms on a Defect-Free MgO(001) Surface

In this contribution, we investigate the interaction between CO and O₂ with metal atoms of group 11 deposited on a defect-free magnesium oxide surface using density functional theory with periodic point charge embedding. We present the first transversal study of the adsorption and coadsorption of CO and O₂ on coinage metal adatoms deposited on metal oxide surfaces from the perspective of single-atom catalysis. Various analysis tools shed light on the binding situation of the metal atoms to the substrate as well as on the situation of the two molecules on the different metal centers. Our analysis demonstrates that cooperative electronic effects enhance the stability of CO upon coadsorption with O₂ for all three metal centers. Our results also explain the lack of catalytic activity of group 11 metal atoms with respect to CO oxidation under thermal conditions as a competition between OC-O₂ bond activation and surface diffusion, leading to metal atom agglomeration. Additionally, it is shown how coadsorption of CO and O₂ on Au/Mg(001) could pave the way to single-atom photocatalysis.

The structural, electronic and catalytic properties of Aun (n = 1–4) nanoclusters on monolayer MoS2

The structural stability, electronic and catalytic properties of Au_n (n = 1–4) nanoclusters supported on monolayer MoS₂ have been investigated based on first principle DFT calculation with van der Waals (vdW) corrections.

Geometric and electronic properties of gold clusters doped with a single oxygen atom

A systematic theoretical study on single oxygen atom doped gold clusters showed that a single oxygen atom can be adsorbed on various sites of gold surfaces, and obtain nearly one electron from gold atoms.

Global minimization of gold clusters by combining neural network potentials and the basin-hopping method

Neural network potentials trained by first-principles density functional theory total energies were applied to search for global minima of gold nanoclusters within the basin-hopping method. Using Au58 as an example, we found a new putative global minimum which has a core-shell structure of Au10@Au48 and C4 symmetry. This new structure of Au58 is 0.24 eV per formula more stable than the best previous model that has C1 symmetry. This work demonstrates that neural network potentials combined with the basin-hopping method could be very useful in global minimization for medium-sized metal clusters which might be computationally prohibitive for first principles density functional theory.

Layered double hydroxide supported gold nanoclusters by glutathione-capped Au nanoclusters precursor method for highly efficient aerobic oxidation of alcohols

M3Al-layered double hydroxide (LDH, M = Mg, Ni, Co) supported Au nanoclusters (AuNCs) catalysts have been prepared for the first time by using water-soluble glutathione-capped Au nanoclusters as precursor. Detailed characterizations show that the ultrafine Au nanoclusters (ca. 1.5 ± 0.6 nm) were well dispersed on the surface of LDH with a loading of Au below ∼0.23 wt% upon synergetic interaction between AuNCs and M3Al-LDH. AuNCs/Mg3Al-LDH-0.23 exhibits much higher catalytic performance for the oxidation of 1-phenylethanol in toluene than Au/Mg3Al-LDH(DP) by the conventional deposition precipitation method and can be applied for a wide range of alcohols without basic additives. This catalyst can also be reused without loss of activity or selectivity. The AuNCs/M(= Ni, Co)3Al-LDH catalysts present even higher alcohol oxidation activity than AuNCs/Mg3Al-LDH. Particularly, AuNCs/Ni3Al-LDH-0.22 exhibits the highest activity (46 500 h(-1)) for the aerobic oxidation of 1-phenylethanol under solvent-free conditions attributed to its strongest Au-support synergy. The excellent activity and stability of AuNCs/M3Al-LDH catalysts render these materials promising candidates for green base-free selective oxidation of alcohols by molecular oxygen.

Communication: Determining the lowest-energy isomer of Au8: 2D, or not 2D

A parallel numerical derivative code, combined with parallel implementation of the coupled-cluster method with singles, doubles, and non-iterative triples (CCSD(T)), is used to optimize the geometries of the low-energy structures of the Au8 particle. The effects of geometry relaxation at the CCSD(T) level and the combined effects of the basis set and core-valence correlations are examined and the results are compared with the corresponding second-order Møller-Plesset perturbation theory calculations. The highest-level computations, in which the single-point CCSD(T) calculations employing the correlation-consistent basis set of the cc-pVTZ quality and the associated relativistic effective core potential (ECP), both optimized for gold, and correlating the 5d(10)6s(1) valence and 5s(2)5p(6) semi-core electrons, are combined with the geometrical information obtained with the corresponding CCSD(T)/cc-pVDZ/ECP approach, favor the planar configuration, with the next three non-planar structures separated by 4-6 kcal/mol. In agreement with the earlier work, smaller-basis set CCSD(T) computations provide unreliable results for the relative energetics, even when the geometries are optimized at the CCSD(T) level.

Charge-dependent trends in structures and vibrational frequencies of [CO-Au-O2](q) (q = -1, 0, +1) complexes: evidence for cooperative interactions

Charge-dependent trends in the structures, vibrational frequencies, and binding energies of binary [AuCO](q) and [AuO(2)](q) and ternary [O(2)AuCO](q) complexes (q = -1,0,+1), have been investigated using density functional theory calculations. Three different geometrical motifs, given descriptive names of "separated", "pre-reactive", and "long-range", are identified for the ternary complexes. For the binary systems, the general trend is that the complexes become more diffuse as the charge becomes more negative, having longer intermolecular bond distances and weaker binding energies. The trends shown by the ternary complexes are more complicated, and are different for the various geometrical motifs. However, a general trend is that there is a cooperative interaction involving both the CO and O(2) with the Au center, which becomes more pronounced as the negative charge on the complexes increases from cationic to neutral to anionic. This cooperative interaction leads to increased electron density on the O(2) moiety, as is reflected in the bond-lengths and vibrational frequencies. Furthermore, it is found that for the pre-reactive complexes, the role of the Au center is to stabilize the formation of a conjugated π-system between the CO and O(2) molecules.

Systematic study of Au6 to Au12 gold clusters on MgO(100) F centers using density-functional theory

We present an optimized genetic algorithm used in conjunction with density-functional theory in the search for stable gold clusters and O2 adsorption ensembles in F centers at MgO(100). For Au8 the method recovers known structures and identifies several more stable ones. When O2 adsorption is investigated, the genetic algorithm is used to imitate structural fluxionality, increasing the O2 bond strength by up to 1 eV. Extending the method to Au(6,10,12), strong O2 adsorption configurations are found for all sizes. However, the effect of fluxionality appears to wear off with increasing cluster size.

Interfacial tension oscillations without surfactant transfer

The dynamic interfacial tension oscillations of different frequency and amplitude were observed by using a pendant drop method for tetraoctyl-, tetradodecyl-, tetrahexadecyl-, and tetraoctadecylammonium bromides at a nitrobenzene/water interface. Despite surfactant mass transfer from the nitrobenzene to the aqueous phase being negligible for these lipophilic derivatives, the oscillations were often accompanied by clouding of the organic phase in the vicinity of the interface. A possible mechanism of the observed phenomena is discussed in relation to spontaneous emulsification at the liquid-liquid interface.

Structure of Ag Clusters Grown on Fs-Defect Sites of an MgO(1 0 0) Surface

The structure of AgN clusters (N=1-4, 6, 8, 10), both in the gas phase and grown on the MgO(1 0 0) surface containing Fs-defects, has been investigated by a density functional basin-hopping (DF-BH) approach. In analogy with what observed in the case of gold clusters, it is found that the presence of the defect implies a double frustration and a cylindrical invariance of the metal-surface interaction, causing small Ag clusters growing around the Fs defect to be highly fluxional. Nevertheless, two different structural crossovers are found to be induced by the metal-defect interaction for the adsorbed clusters such that: 1) planar structures prevail for N<or=4 (as in the gas phase); 2) noncrystalline (fivefold symmetric) structures, which are the lowest energy ones in the gas phase for medium sized AgN clusters (N>or=7), prevail for N=6 and N=8; 3) distorted face-centered cubic (fcc) structures grown pseudomorphically on the defected surface prevail for N=10. The transition from fivefold to fcc motifs is rationalized in terms of the double-frustration effect, which increases the bond strain of the noncrystalline structures. Detrapping energies from the defect were also calculated; the lowest energy pathway corresponds to the detachment of a dimer.

Nature of reactive O2 and slow CO2 evolution kinetics in CO oxidation by TiO2 supported Au cluster

Recent experiments on CO oxidation reaction using seven-atom Au clusters deposited on TiO2 surface correlate CO2 formation with oxygen associated with Au clusters. We perform first principles calculations using a seven-atom Au cluster supported on a reduced TiO2 surface to explore potential candidates for the form of reactive oxygen. These calculations suggest a thermodynamically favorable path for O2 diffusion along the surface Ti row, resulting in its dissociated state bound to Au cluster and TiO2 surface. CO can approach along the same path and react with the O2 so dissociated to form CO2. The origin of the slow kinetic evolution of products observed in experiments is also investigated and is attributed to the strong binding of CO2 simultaneously to the Au cluster and the surface.

Rotational Invariance and Double Frustration in the Structures of Gold Clusters Growing around the Fs-Defected MgO (100) Surface

The interaction of small gold clusters (Au(n), n = 1-4, 20) and a gold monolayer with the MgO (100) surface surrounding a neutral oxygen vacancy (F(s) center) is investigated using density-functional (DF) calculations. It is found that the presence of the defect modifies the interaction of gold not only with the vacancy itself, but also with the oxygen and magnesium atoms around it by increasing both the adhesion energy and the equilibrium bond distances. This is at variance with the interaction of metal atoms with the regular MgO (100) surface or the F(s) defect itself, in which an increase of the adhesion energy is associated with a shortening of the metal-surface distance. The resulting double frustration and cylindrical invariance of the metal-surface interaction cause small gold clusters growing around an F(s) nucleation center to be highly fluxional in terms both of rotational freedom and of multiple competing structural motifs. Fragmentation energies of the gold clusters are also discussed, finding that the lowest-energy pathway corresponds to the detachment of a dimer.

V@Au12-: An Improved Novel Catalyst for CO Oxidation?

The catalytic properties toward CO combustion of an encapsulated cluster, V@Au12-, have been explored by means of plane-wave pseudopotential density-functional theory calculations. Single adsorption of both O2 and CO as well as coadsorption have been considered. The adsorption energy for the O2 molecule is about 0.3-0.4 eV which limits its use to low temperatures. However, in contrast to what happens for pure gold clusters, this system shows a remarkable capacity to bind a high number of oxygen molecules. Moreover, its icosahedral cluster is able to bind 12 CO molecules, since all of the gold atoms are available. The bond between the metal cluster and the oxygen molecule mainly arises from a charge transfer from the metal toward the pi(g) antibonding O2 orbitals, while in the case of CO molecule, the classical sigma-donation pi-back-donation mechanism is observed. Finally, no coadsorption effects are found when both molecules are adsorbed, the interaction properties between the cluster and the substrates remain basically unaltered.