Insights into the structural, electronic and magnetic properties of V-doped copper clusters: comparison with pure copper clusters

CO2 and H2 Activation on Zinc-Doped Copper Clusters

Here we systematically investigate the CO2 and H2 activation and dissociation on small Cun Zn0/+ (n=3-6) clusters using Density Functional Theory. We show that Cu6 Zn is a superatom, displaying an increased HOMO-LUMO gap and is inert towards CO2 or H2 activation or dissociation. While other neutral clusters weakly activate CO2 , the cationic clusters preferentially bind the CO2 in monodentate nonactivated way. Notably, Cu4 Zn allows for the dissociation of activated CO2 , whereas larger clusters destabilize all activated CO2 binding modes. Conversely, H2 dissociation is favored on all clusters examined, except for Cu6 Zn. Cu3 Zn+ and Cu4 Zn, favor the formation of formate through the H2 dissociation pathway rather than CO2 dissociation. These findings suggest the potential of these clusters as synthetic targets and underscore their significance in the realm of CO2 hydrogenation.

Cu n Clusters (n = 13, 43, and 55) as Possible Degradant Agents of mSF6 Molecules (m = 1, 2): A DFT Study

In order to obtain the structural and electronic properties of pristine copper clusters and Cu₁₃-SF₆, Cu₄₃-SF₆, Cu₅₅-SF₆, Cu₁₃-2SF₆, Cu₄₃-2SF₆, and Cu₅₅-2SF₆ systems, DFT calculations were carried out. For Cu₁₃-mSF₆, its surface suffers a drastic deformation, and Cu₄₃-mSF₆ at its outer surface reveals strong interaction for the first chemical molecule; when the second molecule is interacting, these outer surfaces are not severely affected. These two cases degraded fully the first SF₆ molecule; however the second molecule is bonded to the latter systems and for Cu₅₅-mSF₆ (m = 1 and 2) a structural transformation from SF₆ →SF₄ appears as well as inner and outer shells that display slight deformations. The electronic gaps do not exhibit drastic changes after adsorption of mSF₆ molecules, and the magnetic moment remains without alterations. The whole system shows thermal and vibrational stability. In addition, for Cu₁₃-mSF₆ the values of the optical gap and intensity of the optical exhibit changes with respect to the pristine case (Cu₁₃), and the rest of the systems do not exhibit major oscillations. These icosahedral copper clusters emerge as a good option to degrade mSF₆ molecules.

Structural and electronic properties for Be-doped Ptn (n = 1-12) clusters obtained by DFT calculations

In this work, we have performed a computational study on the structure and electronic properties for Be-doped Pt_n (n = 1-12) clusters in the framework of density functional theory (DFT). The most stable structures of the clusters are obtained by a structure search procedure based in simulated annealing. The results show that the Pt_nBe clusters adopt compact structure motifs with Be situated at the edge sites while only in Pt₁₁Be the Be atom occupies the center site. The energetic parameters showed that Pt₅Be, Pt₇Be and Pt₁₀Be are the most stable ones. The Pt_nBe clusters with (n = 5-7) have similar vertical ionization potential (vIP) and vertical electron affinity (vEA) parameters compared to the unary Pt clusters, while Pt₉Be and Pt₁₁Be have the higher vEA values. In particular, the d-band center is slightly higher for the doped clusters, suggesting an enhanced reactivity. The σ-holes are found more remarkable for the doped clusters, which are situated in the Be dopant and low coordinated Pt sites. The data on the infrared spectra of the clusters is also provided and showed a significant blue shift due to the vibrational modes of the Be atom. These results are useful for understanding the fundamental properties of Be-doped Pt_n clusters in the subnanometer region.

Screening of transition metal doped copper clusters for CO2 activation

Activation of CO₂ is the first step towards its reduction to more useful chemicals. Here we systematically investigate the CO₂ activation mechanism on Cu₃X (X is a first-row transition metal atom) using density functional theory computations. The CO₂ adsorption energies and the activation mechanisms depend strongly on the selected dopant. The dopant electronegativity, the HOMO-LUMO gap and the overlap of the frontier molecular orbitals control the CO₂ dissociation efficiency. Our calculations reveal that early transition metal-doped (Sc, Ti, V) clusters exhibit a high CO₂ adsorption energy, a low activation barrier for its dissociation, and a facile regeneration of the clusters. Thus, early transition metal-doped copper clusters, particularly Cu₃Sc, may be efficient catalysts for the carbon capture and utilization process.

Systematic Investigation of the Structure, Stability, and Spin Magnetic Moment of CrM n Clusters (M = Cu, Ag, Au, and n = 2-20) by DFT Calculations

Binary clusters of transition-metal and noble-metal elements have been gathering momentum for not only advanced fundamental understanding but also potential as elementary blocks of novel nanostructured materials. In this regard, the geometries, electronic structures, stability, and magnetic properties of Cr-doped Cu _n , Ag _n , and Au _n clusters (n = 2-20) have been systematically studied by means of density functional theory calculations. It is found that the structural evolutions of CrCu _n and CrAg _n clusters are identical. The icosahedral CrCu₁₂ and CrAg₁₂ are crucial sizes for doped copper and silver species. Small CrAu _n clusters prefer the planar geometries, while the larger ones appear as on the way to establish the tetrahedral CrAu₁₉. Our results show that while each noble atom contributes one s valence electron to the cluster shell, the number of chromium delocalized electrons is strongly size-dependent. The localization and delocalization behavior of 3d orbitals of the chromium decide how they participate in metallic bonding, stabilize the cluster, and give rise to and eventually quench the spin magnetic moment. Moreover, molecular orbital analysis in combination with a qualitative interpretation using the phenomenological shell model is applied to reveal the complex interplay between geometric structure, electronic structure, and magnetic moment of clusters. The finding results are expected to provide greater insight into how a host material electronic structure influences the geometry, stability, and formation of spin magnetic moments in doped systems.

Adsorption and Activation of CO2 on Small-Sized Cu-Zr Bimetallic Clusters

Adsorption and activation of CO₂ is a key step in any chemical reaction, which aims to convert it to other useful chemicals. Therefore, it is important to understand the factors that drive the activation process and also search for materials that promote the process. We employ the density functional theory to explore the possibility of using small-sized bimetallic Cu-Zr clusters, Cu_4-nZr_n, with n = 1-3 for the above-mentioned key step. Our results suggest that after adsorption, a CO₂ molecule preferably resides on Zr atoms or at the bridge and triangular faces formed by Zr atoms in bimetallic Cu-Zr clusters accompanied with its high degree of activation. Importantly, maximum activation occurs when CO₂ is adsorbed on the CuZr₃ cluster. Interestingly, we find that the adsorption energy of CO₂ can be tuned by varying the extent of the Zr atom in Cu-Zr clusters. We rationalize the high adsorption of CO₂ with the increase in the number of Zr atoms using the d-band center model and the concept of chemical hardness. The strong chemisorption and high activation of CO₂ are ascribed to charge migration between Cu-Zr clusters and the CO₂ molecule. We find an additional band in the infrared vibrational spectra of CO₂ chemisorbed on all of the clusters, which is absent in the case of free CO₂. We also observe that the energy barriers for the direct dissociation of the CO₂ molecule to CO and O decrease significantly on bimetallic Cu-Zr clusters as compared to that on pure Cu₄. In particular, the barrier heights are considerably small for Cu₃Zr and CuZr₃ clusters. This study demonstrates that Cu₃Zr and CuZr₃ clusters may serve as good candidates for activation and dissociation of the CO₂ molecule.

Systematic cluster growth: a structure search method for transition metal clusters

The systematic cluster growth (SCG) method is a biased structure search strategy based on a seeding process for investigating the structural evolution and growth pattern of transition metal clusters.

Stability of cationic silver doped gold clusters and the subshell-closed electronic configuration of AgAu14. J Chem Phys 2020;153:244304. [PMID: 33380086 DOI: 10.1063/5.0033487]

Silver doping is a valuable route to modulate the structural, electronic, and optical properties of gold clusters. We combine photofragmentation experiments with density functional theory calculations to investigate the relative stability of cationic Ag doped Au clusters, AgAu_N-1 ⁺ (N ≤ 40). The mass spectra of the clusters after photofragmentation reveal marked drops in the intensity of AgAu₈ ⁺, AgAu₁₄ ⁺, and AgAu₃₄ ⁺, indicating a higher relative stability of these sizes. This is confirmed by the calculated AgAu_N-1 ⁺ (N ≤ 17) dissociation energies peaking for AgAu₆ ⁺, AgAu₈ ⁺, and AgAu₁₄ ⁺. While the stability of AgAu₆ ⁺ and AgAu₈ ⁺ can be explained by the accepted electronic shell model for metal clusters, density of states analysis shows that the geometry plays an important role in the higher relative stability of AgAu₁₄ ⁺. For this size, there is a degeneracy lifting of the 1D shell, which opens a relatively large HOMO-LUMO gap with a subshell-closed 1S²1P⁴1P²1D⁶ electronic configuration.

Quantum-Chemical Design of Molecular Structures of Tetra-, Penta- and Hexanuclear Metal Clusters Containing Aluminum and 3d-Element Atoms

Various data on the structural and thermodynamic characteristics of polynuclear metal clusters containing atoms of aluminum and various d-elements with the general formula Al_nM_m where (n + m) is 4, 5, or 6, and which can be precursors for the formation of nanoparticles of elemental metals or intermetallic compounds, have been systematized and discussed. It has been noted that each of these metal clusters in principle is able to exist in very diverse structural isomers, differing significantly among themselves in terms of the total energy and spin multiplicity of the ground state, the number of which is determined by both the specific values of n and m, and the nature of d-elements in their compositions. The presence of very complex dynamics with respect to the changes of the individual thermodynamic characteristics of the metal clusters under consideration as well as the thermodynamic parameters of the reactions of their formation, depending on the nature of the d-element, were also ascertained. In the main, the given review is devoted to the authors’ works published over the last 10 years. Bibliography – 96 references.

Probing the structural evolution and electronic properties of divalent metal Be2Mgn clusters from small to medium-size

Bimetallic clusters have aroused increased attention because of the ability to tune their own properties by changing size, shape, and doping. In present work, a structural search of the global minimum for divalent bimetal Be₂Mg_n (n = 1-20) clusters are performed by utilizing CALYPSO structural searching method with subsequent DFT optimization. We investigate the evolution of geometries, electronic properties, and nature of bonding from small to medium-sized clusters. It is found that the structural transition from hollow 3D structures to filled cage-like frameworks emerges at n = 10 for Be₂Mg_n clusters, which is obviously earlier than that of Mg_n clusters. The Be atoms prefer the surface sites in small cluster size, then one Be atom tend to embed itself inside the magnesium motif. At the number of Mg larger than eighteen, two Be atoms have been completely encapsulated by caged magnesium frameworks. In all Be₂Mg_n clusters, the partial charge transfer from Mg to Be takes place. An increase in the occupations of the Be-2p and Mg-3p orbitals reveals the increasing metallic behavior of Be₂Mg_n clusters. The analysis of stability shows that the cluster stability can be enhanced by Be atoms doping and the Be₂Mg₈ cluster possesses robust stability across the cluster size range of n = 1-20. There is s-p hybridization between the Be and Mg atoms leading to stronger Be-Mg bonds in Be₂Mg₈ cluster. This finding is supported by the multi-center bonds and Mayer bond order analysis.

Uncovering the structural, electronic and vibrational properties of atomically precise PdmCun clusters and their interaction with CO2 molecule

In this work, we address the structural stability, electronic properties and effect of metal-metal interaction on Raman spectra of icosahedral (Ih) Pd_mCu_n (m + n = 13) clusters using first principles calculations based on dispersion-corrected density functional theory (DFT-D2). Initially, we investigated the relative stability of Ih Pd_mCu_n clusters over monometallic Ih Pd₁₃ and Cu₁₃ clusters by calculating the average binding energy per atom, mixing energy, second order energy difference and average bond length. The Ih Pd₅Cu₈ is the most stable bimetallic cluster with the 2.88 eV, -0.218 eV and 0.678 eV average binding energy per atom, mixing energy and second order energy difference, respectively. The main goals of the present study are to figure out the chemical enhancement, modulation in electronic properties and Pd-Cu bond length in Ih Pd_mCu_n clusters after systematic doping of Cu-atom. Further, to examine the doping effect of Cu atom in Pd cluster, we have also analysed the Raman spectra of Ih Pd_mCu_n clusters. In case of Ih Cu₁₃ cluster, the contraction of Cu-Cu bond length as compared to its bulk form resulted in a significant blue-shift of characteristic Raman peak (212 cm^-1) of Ih Pd₁₃ cluster. Finally, the interaction mechanism of the CO₂ gas molecule over Pd-Cu alloy clusters have also been studied to understand the effect of composition on reactivity of CO₂ gas molecule.

Theoretical Study on the Aggregation of Copper Clusters on a Liquid Surface

The ground state structures of copper clusters with different sizes along with their aggregation have been systematic investigated using Amsterdam Density Functional (ADF) and Atomistix ToolKit (ATK) programs. On the basis of geometry optimization, some Cu clusters with more stable structures which were not reported previously have been revealed. In most cases, these Cu clusters prefer to adopt icosahedral structures which originate from the 13-atom icosahedron. It has also been demonstrated that the interaction between two Cu clusters is anisotropic, which is attributed to their charge distribution, especially the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of Cu clusters. Moreover, we have carried out the simulation of Cu clusters aggregation on the silicone oil substrate by means of Monte Carlo (MC) method, which shows good consistence with our previous experimental studies.

Electrocaloric effect in the two spin-1/2 XXZ Heisenberg edge-shared tetrahedra and spin-1/2 XXZ Heisenberg octahedron with Dzyaloshinskii-Moriya interaction

In the present paper, we consider two species of small spin clusters known as; two spin-1/2 Heisenberg edge-shared tetrahedra and spin-1/2 Heisenberg octahedron with the corresponding Dzyaloshinskii-Moriya terms in a longitudinal magnetic field, then we examine magnetization process and electric polarization of the models as functions of magnetic and electric fields at Low temperature using exact numerical diagonalization. Our exact results are in a good agreement with recent analysis carried out by Strečka and Karľová (2018 AIP Adv. 8 101403); Karľová et al (2017 J. Phys.: Condens. Matter 29 125802). It is demonstrated that the polarization behavior coincides the magnetization curves (including sequential intermediate plateaus), also it reflects the respective stepwise changes of ground-state phase transitions. We find that the polarization has significant effects on the magnetic field dependencies of the magnetization. Furthermore, we investigate other isothermal strategies such as cooling rate, magnetocaloric effect (MCE), as well as, electrocaloric effect (ECE) for both models. Since, new electrocaloric materials with high performance is of great interest and importance in condensed matter physics, here, we report on the ECE of the both aforedescribed spin-1/2 Heisenberg small clusters. We conclude that two spin-1/2 Heisenberg edge-shared tetrahedra is a material with significant reversible temperature change capability under an external electric field compared with the spin-1/2 Heisenberg octahedron, and can be used for cooling/heating process. On the other hand, our exact results obtained by studying the MCE and ECE of the spin-1/2 Heisenberg octahedron prove that this model displays a rich ECE close to the relevant critical points, thus can be considered as a material with rich electrocaloric(magnetocaloric) performance even in the presence of an external electric(magnetic) field. Generally, by comparing both models with each other, we point out that the two spin-1/2 Heisenberg edge-shared tetrahedra is a high performance electrocaloric material rather than spin-1/2 Heisenberg octahedron, while the spin-1/2 Heisenberg octahedron demonstrates greater MCE.