Magnetic properties of CrMnGen (n = 3-20) clusters

Due to the potential applications in next-generation micro/nano electronic devices and functional materials, magnetic germanium (Ge)-based clusters are receiving increasing attention. In this work, we reported the structures, electronic and magnetic properties of CrMnGen with sizes n = 3-20. Transition metals (TMs) of Cr and Mn tend to stay together and be surrounded by Ge atoms. Small sized clusters with n ≤ 8 prefer to adopt bipyramid-based structures as the motifs with the excess Ge atoms absorbed on the surface. Starting from n = 9, the structure with one TM atom interior appears and persists until n = 16, and for larger sizes n = 17-20, the two TM atoms are full-encapsulated by Ge atoms to form endohedral structures. The Hirshfeld population analyses show that Cr atom always acts as the electron donor, while Mn atom is always the acceptor except for sizes 3 and 6. The average binding energies of these clusters increase with cluster size n, sharing a very similar trend as that of CrMnSin (n = 4-20) clusters, which indicates that it is favorable to form large-sized clusters. CrMnGen (n = 6, 13, 16, 19, and 20) clusters prefer to exhibit ferromagnetic Cr-Mn coupling, while the remaining clusters are ferrimagnetic.

Scaling of the permanent electric dipole moment in isolated silicon clusters with near-spherical shape

In silicon clusters a structural transition from prolate to near-spherical structures takes place at a size of about 25-30 atoms. While some of the prolate clusters are very polar, there has been no experimental evidence of the presence of dipole moments in larger silicon clusters with near-spherical shape. By means of electric molecular beam deflection experiments at cryogenic temperatures, it was possible to prove for the first time that Si_N clusters with more than N = 30 atoms are also polar. Interestingly, the dipole moment per atom for clusters in the range between 30 and 80 or 90 atoms is almost constant and amounts to 0.02 D. This unusual behaviour manifests in effective polarizabilities increasing linearly with cluster size. The dipolar contribution to the polarizability means that Si_N clusters with N = 80 atoms can be polarized more than twice as well as a correspondingly small sphere with the dielectric properties of bulk α-Si. This finding is analysed with quantum chemical calculations concerning the geometric structure as well as the charge distribution and is related to the dielectric behaviour of polar semiconductor nanocrystals.

Structural evolution and electronic properties of pure and semiconductor atom doped in clusters: Inn - , Inn Si- , and Inn Ge- (n = 3-16)

The bonding and electronic properties of In_n ^- , In_n Si^- , and In_n Ge^- (n = 3-16) clusters have been computationally investigated. An intensive global search for the ground-state structures of these clusters were conducted using the genetic algorithm coupled with density functional theory (DFT). The ground-state structures of these clusters have been identified through the comparison between simulated photoelectron spectra (PES) of the found lowest-energy isomers and the experimentally measured ones. Doping semiconductor atom (Si or Ge) can significantly change the structures of the In clusters in most sizes, and the dopant prefers to be surrounded by In atoms. There are three structural motifs for In_n X^- (X = Si, Ge, n = 3-16), and the transition occurs at sizes n = 5 and 13. All In_n Si^- and In_n Ge^- share the same configurations and similar electronic properties except for n = 8. Among all above studied clusters, In₁₃ ^- stands out with the largest vertical detachment energy (VDE), HOMO-LUMO gap, (E_b ) and second order energy difference Δ² E due to its closed electronic shell of (1S)² (1P)⁶ (1D)¹⁰ (2S)² (1F)¹⁴ (2P)⁶ . Similarly, the neutral In₁₂ X (X = Si, Ge) clusters are also identified as superatoms but with electronic configuration of (1S)² (1P)⁶ (2S)² (1D)¹⁰ (1F)¹⁴ (2P)⁶ .

Symmetry collapse due to the presence of multiple local aromaticity in Ge244

Understanding the structural changes taking place during the assembly of single atoms leading to the formation of atomic clusters and bulk materials remains challenging. The isolation and theoretical characterization of medium-sized clusters can shed light on the processes that occur during the transition to a solid-state structure. In this work, we synthesize and isolate a continuous 24-atom cluster Ge₂₄⁴⁻, which is characterized by X-ray diffraction analysis and Energy-dispersive X-ray spectroscopy, showing an elongated structural characteristic. Theoretical analysis reveals that electron delocalization plays a vital role in the formation and stabilization of the prolate cluster. In contrast with carbon atoms, 4 s orbitals of Ge-atoms do not easily hybridize with 4p orbitals and s-type lone-pairs can be localized with high occupancy. Thus, there are not enough electrons to form a stable symmetrical fullerene-like structure such as C₂₄ fullerene. Three aromatic units with two [Ge₉] and one [Ge₆] species, connected by classical 2c-2e Ge-Ge σ-bonds, are aligned together forming three independent shielding cones and eventually causing a collapse of the global symmetry of the Ge₂₄⁴⁻ cluster.

Gaining insight on the structural transformations from atomic clusters to bulk materials is challenging. Here the authors synthesize a continuous cluster of germanium Ge₂₄⁴⁻, which can be viewed as two terminal Ge₉ units bridged via a Ge₆ central fragment, and characterize it by several techniques including X-ray diffraction; theoretical analysis indicates the presence of three aligned independent aromatic fragments.

Account of the diversity of tunneling spectra at the germanene/Al(1 1 1) interface

Despite the wealth of tunneling spectroscopic studies performed on silicene and germanene, the observation of a well-defined Dirac cone in these materials remains elusive. Here, we study germanene grown on Al(1 1 1) at submonolayer coverages with low temperature scanning tunneling spectroscopy. We show that the tunnelling spectra of the Al(1 1 1) surface and the germanene nanosheets are identical. They exhibit a clear metallic behaviour at the beginning of the experiments, that highlights the strong electronic coupling between the adlayer and the substrate. Over the course of the experiments, the spectra deviate from this initial behaviour, although consecutive spectra measured on the Al(1 1 1) surface and germanene nanosheets are still similar. This spectral diversity is explained by modifications of the tip apex, that arise from the erratic manipulation of the germanium adlayer. The origin of the characteristic features such as a wide band gap, coherence-like peaks or zero-bias anomalies are tentatively discussed in light of the physical properties of Ge and AlGe alloy clusters, that are likely to adsorb at the tip apex.

Theoretical investigation on the low-energy isomer identification, structural evolution, stability, and electronic properties of Al10-xBex (x = 1-9) nanoalloys

Numerous isomeric equilibrium structures have been identified for the Al_10-xBe_x (x = 1-9) nanoalloy clusters by using the stochastic search procedure in combination with density functional theory calculations. The relative stability and various electronic properties of the lowest-energy Al_10-xBe_x (x = 0-10) clusters have been systematically studied by using the B3LYP and CCSD(T) methods with the aug-cc-pVDZ basis set. The evolution of the binding energies, the second difference in energy, HOMO-LUMO gaps, vertical detachment energies, vertical ionization potentials, vertical electron affinities, and hardness with the increasing number of Be atoms in the most stable Al_10-xBe_x (x = 0-10) clusters demonstrates that the global minimum of Al₈Be₂ cluster possesses a special stability. Thus, the electronic structure of the lowest-energy Al₈Be₂ cluster has been also detected in detail. In addition, it is found that the polarizabilities gradually decrease with increasing number of Be atoms, and the charges always transfer from Al to Be atoms in these nanoalloy clusters. We hope this work could provide helpful insight into the composition-dependent electronic properties of BeAl alloy at the nanoscale, serving as powerful guidelines for future experimental research.

Probing the low-energy structures of aluminum–magnesium alloy clusters: a detailed study

The effect of Mg doping on the growth behavior and the electronic properties of aluminum clusters has been investigated theoretically using the CALYPSO (Crystal structure AnaLYsis by Particle Swarm Optimization) method in combination with density functional theory calculations.