Role of Ga-doping in iron-gallium alloy clusters

The structural and magnetic properties of Fen-mCam （n = 3 - 6, m = 0 - 2; n = 13, m = 0 - 3） alloy clusters have been studied using density functional theory. The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites. The Ca-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters, along with a decrease of the local magnetic moments of Fe atoms around Ca dopants. These findings provide a microscopic insight into Fe-Ga alloys which are well：known magnetostriction materials.

Magnetism of Metals, Alloys and of Clusters of Transition Metal Atoms

A condition for local moment formation in metals derived by Stoddart and March (Ann. Phys. NY 1972 64, 174) is first used to discuss the ferromagnetism of body-centred-cubic Fe. A less detailed discussion is also added on Ni and Co. This leads into a treatment of the non- linear response of such 3d ferromagnets to dilute substitutional impurities. Antiferromagnets responding to local changes in the exchange field caused by such impurities are also studied, Mn in Cr being one such system discussed. The paper concludes with a brief summary of clusters of transition metal atoms, with most attention devoted to Cr and to Mn.

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt_6 clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 （M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn） are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.

Structures,stabilities,and magnetic properties of the Fe_nAu(n=1-12) clusters

The configurations,stabilities,electronic,and magnetic properties of FenAu（n = 1–12） clusters are investigated systematically by using the relativistic all-electron density functional theory with the generalized gradient approximation.The substitutional effects of Au in Fen＋1（n = 1,2,4,5,10–12） clusters are found in optimized structures which keep the similar frameworks with the most stable Fen＋1clusters.And the growth way for FenAu（n = 6–9） clusters is that the Au atom occupies a peripheral position of Fen cluster.The peaks appear respectively at n = 6 and 9 for Fen Au clusters and at n = 5 and 10 for Fen＋1clusters based on the size dependence of second-order difference of energy,implying that these clusters possess relatively high stabilities.The analysis of atomic net charge Q indicates that the charge always transfers from Fe to Au atom which causes the Au atom to be nearly non-magnetic,and the doped Au atom has little effect on the average magnetic moment of Fe atoms in Fen Au cluster.Finally,the total magnetic moment is reduced by 3 μB for each of Fen Au clusters except n = 3,11,and 12 compared with for corresponding pure Fen＋1 clusters.

Theoretical insights into oxygen reduction reaction on Au-based single-atom alloy cluster catalysts

Developing highly active alloy catalysts that surpass the performance of platinum group metals in the oxygen reduction reaction(ORR)is critical in electrocatalysis.Gold-based single-atom alloy(AuSAA)clusters are gaining recognition as promising alternatives due to their potential for high activity.However,enhancing its activity of AuSAA clusters remains challenging due to limited insights into its actual active site in alkaline environments.Herein,we studied a variety of Au_(54)M_(1) SAA cluster catalysts and revealed the operando formed MO_(x)(OH)_(y) complex acts as the crucial active site for catalyzing the ORR under the basic solution condition.The observed volcano plot indicates that Au_(54)Co_(1),Au_(54)M_(1),and Au_(54)Ru_(1) clusters can be the optimal Au_(54)M_(1) SAA cluster catalysts for the ORR.Our findings offer new insights into the actual active sites of AuSAA cluster catalysts,which will inform rational catalyst design in experimental settings.

Tailoring optical and photocatalytic properties by single-Ag-atom exchange in Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8) nanoclusters

Precise mono-doping of metal atom into metal particles at a specific particle position(e.g.,the central site)in a highly controllable manner is still a challenge.In this work,we develop a highly controllable strategy for exchanging a single Ag atom into the central gold site of Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8)(Ph=phenyl)nanoclusters.Interestingly,a“pigeon-pair”cluster of{[Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8)]·[Au_(12)Ag_(13)(PPh_(3))_(10)C_(l8)]}^(2+)is obtained and confirmed by electrospray ionization mass spectrometry(ESI-MS),thermogravimetric analysis(TGA)and single crystal X-ray diffraction(SCXRD)analysis.The experimental results and density functional theory(DFT)calculations suggest that the single-metal-atom exchanging from[Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8)]^(+)to[Au_(12)Ag_(13)(PPh_(3))_(10)C_(l8)]^(+)occurs at the central position through the side entry of theμ_(3)-bridging Cl atoms.Finally,the effects on the electronic structure and properties caused by the single-atom exchange at the central site are shown by the enhancement of fluorescence and catalytic activity in the photocatalytic oxidation of ethanol.

Influence of electric field on the quenched-in vacancy and solute clustering during early stage ageing of Al-Cu alloy

The effects of electric field on the evolution of excess quenched-in vacancy as well as solute clustering in Al-4wt%Cu alloy, and on the vacancy migration and formation enthalpy of pure aluminum were investigated, using positron annihilation lifetime spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, transmission electron microscopy, hardness measurement and four-probe electrical resistivity measurement. The results showed that the electric field improved age hardening response obviously and postponed the decay of excess vacancies for 30rain during the early stage ageing of Al-4wt%Cu alloy. A large number of 2-4nm GP zones with dense distribution were observed after 1 min ageing with an electric field applied. The electric field-assisted-aged sample owned a lower coarsening rate of GP zone, which was about three fifths of that in the aged sample without an electric field, from 1 min to 120 rain ageing. The electric field contributed 8% increase of the vacancy migration enthalpy （0.663 ±0.021 eV） of pure Al, comparing with that （0.611 ±0.023 eV） of pure Al without an electric field. The increase of vacancy migration enthalpy, induced by the electric field, was responsible for the difference on evolution of quenched-in vacancy, rapid solute clustering and age hardening improvement during the early stage ageing of Al-4wt%Cu alloy.

Theoretical Study on Structural Stability of Alloy Cages:A Case of Silicon-Doped Heterofullerenes

Structural stability and Si-substitution pattern in fullerene cage of C_(60−n)Sin are thoroughly investigated by integrating density functional calculations with a colorbond graph(CBG)model.We find that the parameterized CBG model with genetic algorithms can efficiently scan the large configuration space of alloy and therefore identify the low-energy region within the first-principles accuracy.Low-energy(stable)structures of C_(60−n)Sin in carbon-rich region(1≤n≤30)were identified and the silicon atoms are found to tend to aggregate in the fullerene cage.The mixing energy of these low-energy structures is ~35 meV/atom and insensitive to the Si concentration.We expect that these alloy fullerene cages can be synthesized experimentally at elevated temperatures.

Density functional theory calculations of lithium alloying with Ge_(10)H_(16) atomic cluster

We exploited a hydrogen-passivated germanium atomic cluster（Ge10H16） as a model to study the mechanism of lithium alloying with germanium. Based on the density functional theory, the electronic and crystal structures of lithium-alloyed Ge10H16 were investigated. The theoretical results indicate that the alloying of lithium with Ge10H16 will weaken the germanium-hydrogen bond and repel the closest germanium atom away from the alloyed lithium atom. Based on the maps of the electron density distribution, the nature of the lithium-germanium chemical bond was analyzed. Moreover, the diffusion process of the lithium on the Ge10H16 cluster was detected, which suggested that there is a close relationship between the diffusion barriers and the coordination number around the lithium atom.

Density Functional Theory and Tight Binding-Based Dynamical Studies of Carbon Metal Systems of Relevance to Carbon Nanotube Growth

Density functional theory(DFT)and tight binding(TB)models have been used to study systems containing single-walled carbon nanotubes(SWNTs)and metal clusters that are of relevance to SWNT growth and regrowth.In particular,TB-based Monte Carlo(TBMC)simulations at 1000 or 1500 K show that Ni atoms that are initially on the surface of the SWNT or that are clustered near the SWNT end diffuse to the nanotube end so that virtually none of the Ni atoms are located inside the nanotube.This occurs,in part,due to the lowering of the Ni atom energies when they retract from the SWNT to the interior of the cluster.Aggregation of the atoms at the SWNT end does not change the chirality within the simulation time,which supports the application of SWNT regrowth(seeded growth)as a potential route for chirality-controlled SWNT production.DFT-based geometry optimisation and direct dynamics at 2000 K show that Cr and Mo atoms in Cr5Co50 and Mo5Co50 clusters prefer to be distributed in the interior of the clusters.Extension of these calculations should deepen our understanding of the role of the various alloy components in SWNT growth.