Recent progress in theoretical and experimental studies of metal-doped silicon clusters: Trend among elements of periodic table

Discovery of a series of silicon-based ferrimagnets in CrMnSin (n = 4-20) clusters

Herein, the structural evolution, electronic and magnetic properties of silicon clusters with two different dopants, CrMnSin (n = 4-20) clusters were investigated at density functional theory (DFT) level. Small-sized CrMnSin (n = 4-9) clusters tend to adopt bipyramid-based geometries, while clusters with sizes n = 10 and 11 prefer to opening cage-like structures. For sizes n = 12 to 14, the half-encapsulated structures gradually transform into closed-cage Cr@Sin structures, with the Mn atom exposed outside. Starting from size 15, both the Cr and Mn atoms are completely encapsulated by silicon atoms. Meanwhile, the Cr and Mn atoms in smaller-sized CrMnSin (n = 4-7) clusters tend to be separated, while they prefer to stay together for larger sizes. Cr atom always acts as electron donor, but not for Mn atom. From the average binding energies, one can conclude that it is easier to form larger size clusters. Smaller and larger sized CrMnSin (n = 4-9 and 19-20) clusters prefer to exhibit ferromagnetic Cr-Mn coupling, while sizes n = 10-18 always exhibit ferrimagnetic state. To our knowledge, the CrMnSin clusters is the first kind of neutral transition-metal doped semiconductor clusters that show ferrimagnetic state within a wide size range.

Polysiloxane-Based Molecular Logic Gate for Dual-Channel Visualizing Mitochondrial pH and Sulphite Changes during Cuproptosis

Intracellular Cu-induced regulated cell death, characterized by the aggregation of lipidizing mitochondrial enzymes, is called cuproptosis. Mitochondria play a vital role in the metabolic regulation of cell injury and stressful immune responses. The pH levels and sulfur dioxide (SO2) content in mitochondria have important indicative roles in the regulation of cuproptosis. However, fluorescent probes that simultaneously detect changes in pH and SO2 in mitochondria during cuprotosis have not been reported. To fill this blank, in this study, we dexterously used functional polysiloxane as a fluorescent platform to propose a molecular logic gate probe P0-pH-SO2 for detecting changes in intramitochondrial pH and SO2 content through a dual-channel mode. In addition, we defined a new function to reflect the cellular state of the elesclomol-induced cuproptosis process based on the input and output of the relevant logic relationship. This new fluorescent molecular logic gate probe P0-pH-SO2 can be rapidly activated by mitochondrial sulfites to induce green fluorescence, while the red fluorescence is quenched with the proton in the mitochondria. Overall, this study developed a novel logic-gated molecular probe that provided a versatile strategy for monitoring the role played by intramitochondrial sulfites and H+ in cuproptosis. This work will open the way to broaden the applications of molecular logic gates and fluorescent polysiloxanes.

Structural Evolution and Electronic Properties of V2Sin-/0 (n = 7-14) Clusters: Anion Photoelectron Spectroscopy and Theoretical Calculations

A systematic study of the structures and electronic properties of V2-doped silicon clusters, V2Sin-/0 (n = 7-14), was carried out by anion photoelectron spectroscopic experiments combined with theoretical calculations. According to the experimental spectra of V2Sin- (n = 7-14) clusters, the V2Si12- cluster has the highest vertical detachment energy (VDE) of 3.66 eV, while V2Si7- and V2Si14- clusters have lower VDEs of 2.81 and 2.84 eV, respectively. The most stable structure searches find that two V atoms in the V2Sin- clusters with size n = 7 and 8 are located at the surface, while V2Sin- clusters with n ≥ 9 prefer cage-like structures. Based on the analysis of the structural evolution of V2Sin- (n = 9-14) clusters, it can be clearly seen how the antihexagonal prism with one V encapsulated in the cage is gradually built from n = 9 to 12 and further developed from n = 12 to 14 with the extra silicon atoms located at the surface of the Si12 cage. The molecular orbital and the atoms in molecule analysis of the V2Sin- (n = 7-14) anions demonstrate that the strong V-V bond and the delocalized interaction between the V2 moiety and the Sin ligand play a significant role in stabilizing the cluster structures. A strong linear correlation has been found between the Wiberg bond order of the V-V bond and the electron density at the V-V bond critical points.

Making Sense of the Growth Behavior of Ultra-High Magnetic Gd2-Doped Silicon Clusters

The growth behavior, stability, electronic and magnetic properties of the Gd₂Si_n^- (n = 3-12) clusters are reported, which are investigated using density functional theory calculations combined with the Saunders 'Kick' and the Artificial Bee Colony algorithm. The lowest-lying structures of Gd₂Si_n^- (n = 3-12) are all exohedral structures with two Gd atoms face-capping the Si_n frameworks. Results show that the pentagonal bipyramid (PB) shape is the basic framework for the nascent growth process of the present clusters, and forming the PB structure begins with n = 5. The Gd₂Si₅^- is the potential magic cluster due to significantly higher average binding energies and second order difference energies, which can also be further verified by localized orbital locator and adaptive natural density partitioning methods. Moreover, the localized f-electron can be observed by natural atomic orbital analysis, implying that these electrons are not affected by the pure silicon atoms and scarcely participate in bonding. Hence, the implantation of these elements into a silicon substrate could present a potential alternative strategy for designing and synthesizing rare earth magnetic silicon-based materials.

Electron Detachments of NbSin-/0 (n = 1-3) Clusters from Density Matrix Renormalization Group-CASPT2 Calculations

The electronic states of NbSi_n^-/0/+ (n = 1-3) clusters have been explored using the state-of-the-art DMRG-CASPT2 method with relatively large active spaces. The leading configurations, bond distances, vibrational frequencies, and relative energies of the low-lying states were identified. Electron detachment energies of the anionic cluster and ionization energies of the neutral clusters were reported at the DMRG-CASPT2 level. The ground states of the NbSi_n^-/0/+ (n = 1-3) clusters were predicted as the ³Δ, ⁴Π, and ⁵Π states of the linear NbSi^-/0/+, the ³A₂, ⁴B₁, and ³B₁ states of cyclic NbSi₂^-/0/+, and the ¹A', ²A', and ³A″ states of tetrahedral NbSi₃^-/0/+ isomers. The first feature in the photoelectron spectrum of NbSi^- was attributed to the transitions from the anionic ³Δ ground state to the neutral ⁴Π, ⁴Δ, and ⁴Φ states, whereas the second feature was assigned to the transitions to the neutral ²Δ, ²Σ⁺, and ²Φ states. The first band in the photoelectron spectrum of NbSi₃^- was ascribed to the transition from the anionic ¹A' ground state to the neutral 1²A' and 1²A″ states; the second band was attributed to the transitions to 2²A', 2²A″, and 3²A' states; and the third band was assigned to the transition to 3²A' states.

Understanding the Stability of an Unprecedented Si-Be Bond within Quantum Confinement

As of today, the Si-Be bond remains underexplored in the literature, and therefore its anomalous behavior continues to be an unsolved puzzle to date. Therefore, the present study aims at evaluating the integrity of an unprecedented Si-Be bond within quantum confinement. To accomplish this, first-principles-based calculation are performed on Be-doped silicon clusters with atomic sizes 6, 7, and 10. Silicon clusters are sequentially doped with one, two, and three Be atoms, and their thermal response is registered in the temperature range of 200-1500 K, which discloses several research findings. During the course of the simulations, the clusters face various thermal events such as solid cluster phase, rapid structural metamorphosis, and fragmentation. Si-Be nanoalloy clusters are noted to be thermally stable at lower temperatures (200-700 K); however, they begins to disintegrate earlier at a temperature as low as 800 K. This lower stability is attributed to the weak nature of Si and Be heteroatomic interactions, which is corroborated from the structural and electronic property analysis of the doped clusters. In addition to this, the performance of Be-doped clusters at finite temperatures is also compared with the thermal response of two other popular systems, viz., C- and B-doped silicon clusters.

Superatomic states under high pressure

The study of superatoms has attracted great interest since they apparently go beyond the traditional understanding of the periodic table of elements. In this work, we clearly show that superatoms can be extended from conventional structures to states under pressure condition. By studying the compression process of the CH₄@C₆₀ system formed via embedding methane molecules inside fullerene C₆₀, it is found that the system maintains superatomic properties in both static states, and even dynamic rotation situations influenced by quantum tunneling. Remarkably, the simulations reveal the emergence of new superatomic molecular orbitals by decreasing the confined space to approach the van der Waals boundary between CH₄ and C₆₀. Our current results not only establish a complete picture of superatoms from ambient condition to high pressure, but also offer a perspective for the discovery and exploration of new properties in superatom systems under extreme conditions.

Bridging the gas and condensed phases for metal-atom encapsulating silicon- and germanium-cage superatoms: electrical properties of assembled superatoms

With the development of nanocluster (NC) synthesis methods in the gas phase, atomically precise NCs composed of a finite number of metal and semiconductor atoms have emerged. NCs are expected to be the smallest units for nanomaterials with various functions, such as catalysts, optoelectronic materials, and electromagnetic devices. The exploration of a stable NC called a magic number NC has revealed a couple of important factors, such as a highly symmetric geometric structure and an electronic shell closure, and a magic number behavior is often enhanced by mixing additional elements. A synergetic effect between geometric and electronic structures leads to the formation of chemically robust NC units called superatoms (SAs), which act as individual units assembled as thin films. The agglomeration of non-ligated bare SAs is desirable in fabricating the assembled SAs associated with intrinsic SA nature. The recent development of an intensive pulsed magnetron sputtering method opens up the scalable synthesis of SAs in the gas phase, enabling the fabrication of SA assembly coupled with the non-destructive deposition of a soft-landing technique. This perspective describes our recent progress in the investigation of the formation of binary cage SA (BCSA) assembled thin films composed of metal-atom encapsulating silicon-cage SAs (M@Si₁₆) and germanium-cage SAs (M@Ge₁₆), with a focus on their electrical properties associated with a conduction mechanism toward the development of new functional nanoscale materials.

Structures and electronic properties of VSin- (n = 14-20) clusters: a combined experimental and density functional theory study

We present a systematic study of the structures and electronic properties of vanadium-doped silicon cluster anions, VSi_n^- (n = 14-20), by combining photoelectron spectroscopy (PES) measurements and density functional theory (DFT) based theoretical calculations. High resolution PES of low temperature (10 K) clusters are acquired at a photon wavelength of 248 nm. Low-lying structures of VSi_14-20^- are obtained by a genetic algorithm based global minimum search code combined with DFT calculations. Excellent agreement is found between the measured PES and the simulated electron density of states of the putative ground-state structures. We conclude that clusters with sizes n = 14 and n = 15 prefer cage-like structures, with the encapsulated vanadium atom bonding with all silicon atoms, while a fullerene-like motif is more favorable for n ≥ 16. For the sizes n = 16 to 19, the structures consist of a V@Si₁₄ with two, three, four, and five Si atoms on the surface of the cage. For n = 20 the structure consists of a V@Si₁₅ with five Si atoms on the surface of the cage. VSi₁₄^- has the highest stability and stands out as a simultaneous closing of electronic and geometrical shells.

Electronic States of CoSin-/0/+ (n = 1-3) Clusters from Density Matrix Renormalization Group-CASPT2 Calculations

Density matrix renormalization group-CASPT2 (DMRG-CASPT2), CASPT2, and density functional theory are employed to describe the complicated geometrical and electronic structures of CoSi_n^-/0/+ (n = 1-3) clusters. The active spaces of DMRG-CASPT2 are extended to 23 orbitals. The DMRG-CASPT2 method with such large active spaces is reasonable to provide highly accurate relative energies of the electronic states. The pure BP86, PBE, and TPSS functionals appear to be suitable to compute the relative energies of the electronic states of cobalt-doped silicon clusters. The leading configurations, bond distances, vibrational frequencies, normal modes, and relative energies of the electronic states are reported. The electron detachment energies of the removals of one electron from the anionic and neutral clusters are estimated. All six bands in the photoelectron spectrum of CoSi₃^- are interpreted based on the computed electron detachment energies and Franck-Condon factor simulations.

Li8 Si8 , Li10 Si9 , and Li12 Si10 : Assemblies of Lithium-Silicon Aromatic Units

We report the global minima structures of Li₈ Si₈ , Li₁₀ Si₉ , and Li₁₂ Si₁₀ systems, in which silicon moieties maintain structural and chemical bonding characteristics similar to those of their building blocks: the aromatic clusters T_d -Li₄ Si₄ and C_2v -Li₆ Si₅ . Electron counting rules, chemical bonding analysis, and magnetic response properties verify the silicon unit's aromaticity persistence. This study demonstrates the feasibility of assembling silicon-based nanostructures from aromatics clusters as building blocks.

Study on the growth behavior and photoelectron spectroscopy of neodymium-doped silicon nanoclusters NdSin0/- (n = 8-20) with a double-hybrid density functional theory

Structural evolution, magnetic moment, and thermochemical and spectral properties of NdSi_n^0/- (n = 8-20) nanoclusters were studied. Optimized structures for NdSi_n demonstrated that the configuration with quintet ground state prefers Nd-substituted for a Si of the most stable Si_n + 1 (n = 8-11) structure to Nd-linked configuration with Si₉ tricapped trigonal prism subcluster (n = 12-19). Finally, the configuration prefers to Nd-encapsulated into Si cage framework (n = 20). For anion, the evolution at the quartet state prefers Nd-linked structure for n = 8-19 (excluded 9), and prefers Nd-encapsulated structure of n = 20. The spectral information including electron affinity, vertical detachment energy, and simulated photoelectron spectroscopy were also observed. The 4f electrons of Nd atom in NdSi_n with n = 8-10 hardly participate in bonding, but take part in remaining neutral clusters and all anionic NdSi_n^- clusters. The calculations of average bond energy, HOMO-LUMO gap, and chemical bonding analyses reveal that NdSi₂₀^- possesses perfect thermodynamic and ideal chemical stability, making it as the most appropriate constitutional units for novel multi-functional semiconductors.

Structure and Stability of a Trefoil Leaf Motif of Metal-Doped Silicon and Germanium Clusters: M3@E20 with E = Si and Ge and M = Fe, Ru, and Os

The first trefoil leaf-shaped cluster, a novel structural motif, was discovered by quantum chemical computations using density functional theory methods for both binary M₃@E₂₀ silicon and germanium clusters in which a metallic M₃ cycle is encapsulated within a D_3h Si₂₀ or Ge₂₀ cage. The triatomic transition metal Fe₃, Ru₃, and Os₃ cycles exhibit a suitable size to be placed inside both Si and Ge cages and satisfy electronic conditions, which thermodynamically stabilize the mixed clusters. Stabilizing orbital interactions between the M₃ cycle and D_3h E₂₀ cage crucially contributes to the high stability of the resulting M₃@E₂₀ trefoil cluster. The novel trefoil leaf-shaped clusters can be used as building units to create different nanoassemblies.