Structure and Magnetism of Neutral and Anionic Palladium Clusters (original) (raw)
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Magnetic properties of Pd atomic clusters from different theoretical approaches
European Physical Journal D, 2007
We report a comparative study of the magnetic properties of free-standing PdN clusters (2 ≤ N ≤ 21) obtained through two different theoretical approaches that are extensively employed in electronic structure calculations: a semi-empirical Tight-Binding (TB) model and an ab-initio DFT pseudopotential model. Conclusions are drawn about the reliability of the TB model for the investigation of the electronic structure and magnetic properties of such complex 4d Transition Metals (TM) systems and we compare the results with previous systematic DFT calculations and comment on some available experiments in the literature. PACS. 75.75.+a Magnetic properties of nanostructures -36.40.Cg Electronic and magnetic properties of clusters -75.50.-y Studies of specific magnetic materials
The structure and properties of small Pd clusters
Nanotechnology, 2008
The zero-temperature minimal energy structure of small free-standing Pd clusters (14 N 21, where N is the number of atoms in the cluster), their characteristics and their magnetic configurations are investigated. Results obtained using five different phenomenological many-body potentials (implemented in combination with a genetic algorithm search) are refined by means of various density functional theory (DFT) techniques. The agreement and differences between the results obtained with our procedure, using these five potentials, are displayed in detail. While phenomenological potentials yield values that approach the minimal energies of larger clusters, as compared with DFT results, they fail to predict the right symmetry group for some of the clusters with N > 14. We find that the minimal energy configurations are not necessarily associated with high symmetry of the atomic arrangement. Actually, several cases of previously overlooked low symmetry structures turn out to have lower energies than more symmetric ones.
We performed an unbiased structure search for low-lying energetic minima of neutral and charged palladium Pd n Q (n = 2-20, Q = 0, + 1 and-1) clusters using CALYPSO method in combination with density functional theory (DFT) calculations. The main candidates for the lowest energy neutral, cationic and anionic clusters are identified, and several new candidate structures for the cationic and anionic ground states are obtained. It is found that the ground state structures of small palladium clusters are more sensitive to the charge states. For the medium size Pd n 0/+/-(n = 16-20) clusters, a fcc-like growth behavior is found. The structural transition from bilayer-like structures to cage-like structures is likely to occur at n = 14 for the neutral and cationic clusters. In contrast, for the anionic counterparts, the structural transition occurs at Pd 13-. The photoelectron spectra (PES) of palladium clusters are simulated based on the time-dependent density functional theory (TD-DFT) method and compared with the experimental data. The good agreement between the experimental PES and simulated spectra provides us unequivocal structural information to fully solve the global minimum structures, allowing for new molecular insights into the chemical interactions in the Pd cages. There is active interest in the synthesis and electrochemical applications of palladium-based nanomaterials 1. Of particular commercial potential is the replacement of platinum-based electrocatalysts with palladium-based ones. Overall, palladium clusters have attracted considerable attention in recent years. Fields of particular interest are hydrogen storage 2 , catalysis 3,4 , sensors 5 and biomedicine 6. Clusters are considered a new and challenging kind of molecular architecture, enabling the transition from few-atom assemblies, to nanoparticles and the bulk. Molecular science is facing unique problems, especially in the determination of stable structures and therefore explanations of the variation of the physicochemical properties. Several experiments 7-9 confirm that small palla-dium clusters exhibit a novel ferromagnetism, although there is no magnetic moment both in the atomic state and in the bulk, due to the closed shell electronic (4d 10 5s 0) configuration of the atom. Recent breakthrough work 10-12 clearly suggests that synthesized subnanometer palladium clusters can be stabilized. In practice, they exhibit enhanced catalytic properties in synthesis and in situ characterization methods of ultra-small metal clusters. Understandably, the stability of the molecular architectures and their electronic configuration is seen as a very important in the study of the ground state of palladium clusters. The growth behavior and respective patterns of palladium clusters have been systematically studied. Kumar et al. 13 presented an icosahedral growth pattern for neutral palladium clusters (n = 2-23, 55 and 147). Futschek et al. 14 investigated the structure of small Pd n (n = 2-13) clusters and suggested that the favorable structures of Pd 11 , Pd 12 and Pd 13 clusters are the fcc fragments of bulk palladium. Zhang et al. 15 examined closely four types of possible structural motifs (fcc like, decahedron based, icosahedron based and prolate ellipsoid-based) and advanced the view that medium-sized Pd n (n = 15-25) clusters prefer fcc-like structures. The case of the Pd 13 cluster merits
Pragya Darshan प्रज्ञा दर्शन, 2023
This work presents a systematic study of the geometric, electronic and magnetic properties of Pd clusters pristine and mono-and bidoped with Mn: Pdn, Pdn−1Mn, Pdn−2Mn 2 where n ≤13. We have used the density functional formalism with the spin polarized generalized gradient approximation. From the variety of possible structures with thirteen atoms, we found the icosahedral configuration to be the most stable as compared to the hexagonal, cub-octahedral and buckled bi-planar. The change in magnetic behavior of Pd clusters after doping with Mn has been observed. This communication is an attempt to understand that behaviour.
Scientific reports, 2016
We performed an unbiased structure search for low-lying energetic minima of neutral and charged palladium Pdn(Q) (n = 2-20, Q = 0, + 1 and -1) clusters using CALYPSO method in combination with density functional theory (DFT) calculations. The main candidates for the lowest energy neutral, cationic and anionic clusters are identified, and several new candidate structures for the cationic and anionic ground states are obtained. It is found that the ground state structures of small palladium clusters are more sensitive to the charge states. For the medium size Pdn(0/+/-) (n = 16-20) clusters, a fcc-like growth behavior is found. The structural transition from bilayer-like structures to cage-like structures is likely to occur at n = 14 for the neutral and cationic clusters. In contrast, for the anionic counterparts, the structural transition occurs at Pd13(-). The photoelectron spectra (PES) of palladium clusters are simulated based on the time-dependent density functional theory (TD-DF...
Twining effects in the magnetism of small Pd clusters
Solid State Communications, 2005
We report a theoretical study of the magnetic behavior of symmetrical twined Pd N (N%220) clusters. The twined Pd N particles were built from two equal Pd M seed-clusters with fcc-like structure for MZ38, 55, 79 and 116. The optimized geometrical structures of Pd N (with N!2M) were obtained from an uniform relaxation of the fcc-like twined configurations using the embedded atom method (EAM). The spin-polarized electronic structure and related magnetic properties of those optimized geometries were calculated by solving self-consistently a spd tight-binding Hamiltonian. We observe that, in some cases the twining process may induce and/or enhance the magnetic moment of the clusters even in the case when the seedclusters are non-magnetic. Our results also suggest a strong dependence on the twining orientation, providing further support to the influence of symmetry effects on the magnetic properties of finite transition-metal systems. We discuss our results in comparison with some recent experimental observations for Pd nanoparticles [
Quantum chemical study of neutral and single charged palladium clusters
Journal of Molecular Catalysis A: Chemical, 2000
The extended Huckel EH method with an electrostatic two-body correction, has been used in order to determine thë structures of small single charged Pd clusters with n s 2-13 and to compare them with the neutral ones. The results for n Ž . Pd and Pd are compared with density functional DFT calculations. Both cation and anion formations were found to 2 3 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 4 d-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. q
Metallic behavior of Pd atomic clusters
Nanotechnology, 2007
We report a study of the nonmetal-metal transition of free-standing PdN clusters (2 ≤ N ≤ 21) carried out through two different theoretical approaches that are extensively employed in electronic structure calculations: a semi-empirical Tight-Binding (TB) model and an ab-initio DFT pseudopotential model. The calculated critical size for the metallic transition decreases fast with the temperature and an oscillatory dependence with the cluster size is obtained particularly in the DFT approach. TB model describes well the metallic behavior for cluster sizes beyond N ≈ 12. Our obtained critical size at room temperature is of the order of the experimental estimation.
Collinear versus noncollinear magnetic order in Pd atomic clusters:Ab initiocalculations
Physical Review B, 2006
We present a thorough theoretical assessment of the stability of non-collinear spin arrangements in small palladium clusters. We generally find that ferromagnetic order is always preferred, but that antiferromagnetic and non-collinear configurations of different sorts exist and compete for the first excited isomers. We also show that the ground state is insensitive to the choice of atomic configuration for the pseudopotential used and to the approximation taken for the exchange and correlation potential. Moreover, the existence and relative stability of the different excited configurations also depends weakly on the approximations employed. These results provide strong evidence on the transferability of pseudopotential and exchange and correlation functionals for palladium clusters as opposed to the situation found for the bulk phases of palladium.
Structures and energetics Of Pd n ( n=2–20) clusters using an embedded-atom model potential
Surface Science, 2002
We have studied the structure and energetics of the stable isomers of Pd n (n ¼ 2-20) clusters by using molecular dynamics and slow-quenching techniques. Cohesion of the clusters is modeled by an embedded-atom potential due to Voter and Chen, which contains many-body atomic interactions. The isomers' statistics are obtained from 10 000 independent initial configurations, which have been generated along a high-energy trajectory (the chosen energy value is high enough to melt the cluster). The internal kinetic energy of these initial conditions is removed slowly. Because of this slow minimization process the locally stable isomers are separated from those meta-stable ones. Probabilities belonging to sampling the basins of attractions of each isomer are computed, and compared with each other. Furthermore, the spectrum, which is formed by isomers' energies, is analyzed. Ó