Revisit of large-gap Si16 clusters encapsulating group-IV metal atoms (Ti, Zr, Hf)

Luminescence properties of endohedrally doped group-IV clusters

Endohedrally doped clusters form a large category of cage clusters, with unique structures, diverse elemental compositions, and highly tunable electronic structures and physisochemical properties. They have been widely achieved in laboratory and may serve as functional building blocks for assembling new supermolecular structures and devices. In this paper, for the first time, we disclosed the luminescence properties of endohedrally doped group-IV clusters by time-dependent density functional theory calculations. A total of 64 cage clusters have been explored in terms of stability, emission wavelength, and the energy difference between the first excited singlet and triplet states. The key geometric and electronic factors governing the photophysical properties of these cage clusters were unveiled, to provide crucial insights for crafting atomically precise nanoclusters for optical and optoelectronic applications.

Alkaline Earth Metal Superatom of W@Si16: Characterization of Group 6 Metal Encapsulating Si16 Cage on Organic Substrates

Transition metal atom (M)-encapsulating silicon cage nanoclusters (M@Si16) exhibit a superatomic nature, depending on the central M atom owing to the number of valence electrons and charge state on organic substrates. Since M@Si16 superatom featuring group 4 and 5 transition metal atoms exhibit rare-gas-like and alkali-like characteristics, respectively, group 6 transition metal atoms are expected to show alkaline earth-like behavior. In this study, M@Si16, comprising a central atom from group 6 (MVI = Cr, Mo, and W) were deposited on C60 substrates, and their electronic and chemical stabilities were investigated in terms of their charge state and chemical reactivity against oxygen exposures. In comparison to alkali-like Ta@Si16, the extent of charge transfer to the C60 substrate is approximately doubled, while the oxidative reactivity is subdued for MVI@Si16 on C60, especially for W@Si16. The results show that a divalent state of MVI@Si162+ appears on the C60 substrate, which is consistently calculated to be a symmetrical cage structure of W@Si162+ in C3v, revealing insights into the "periodic law" of M@Si16 superatoms pertaining to the characteristics of alkaline earth metals.

Role of Partial Vacancy and Structural Distortion in the Stability of Nonstoichiometric Phases Ni7-δInSe2-xSx (1.26 ≥ δ ≥ 0.94; 0 ≤ x ≤ 1.33)

This study explores the structure and stability of partly disordered sulfur-substituted Ni5.74InSe2 (I4/mmm, a = 3.6766(1) Å, c = 18.8178(10) Å, Z = 2). The structure of Ni7-δInSe2-xSx (x = 0.2, 0.36, 0.66, 0.80, 0.94) compounds is isotypic to their parent Ni5.74InSe2 and can be viewed as alternating heterometallic Cu3Au-type ∞2[Ni3In] slabs and defective Cu2Sb-type ∞2[Ni4-δ(Se/S)2] slabs along the [001]-axis. Similar to the parent Se-compound, the Ni-Ch (Ch = chalcogen) fragment is non-stoichiometric and possesses a partially occupied Ni-site. It was observed that with sulfur insertion at the selenium site of Ni5.74InSe2, the interatomic distance between the partially occupied nickel and mixed (S/Se) sites decreases from ∼2.24 to ∼1.95 Å, and the occupancy of the disordered nickel site simultaneously increases. The limiting composition Ni6.06InSe0.67S1.33 (x = 1.33, δ = 0.94) is formed in the sulfur-rich region. Its average structure resembles the Ni6SnS2-type and has a similar motif to Ni5.74InSe2; the only difference is that Cu3Au-type ∞2[Ni3In] alternates with two types of Ni-Ch fragments (Cu2Sb or Li2O type units). By using first-principles electronic structure calculations, we explained the presence of partially disordered nickel sites in the Ni-Ch fragment and rationalized why the nickel site occupancy increases with sulfur insertion.

On the possibility of using the Ti@Si16 superatom as a novel drug delivery carrier for different drugs: A DFT study

The potential application of an experimentally synthesized superatom Ti@Si₁₆ as a novel drug carrier for cisplatin (DDP), isoniazid (INH), acetylsalicylic acid (ASA), 5-fluorouracil (5-Fu), and favipiravir (FPV) has been explored by density functional theory. It is observed that the Pt atom of DDP can be effectively absorbed on Ti@Si₁₆ via a "donation-back donation" electron transfer mechanism, resulting in a moderate adsorption energy of -19.95 kcal/mol for DDP@[Ti@Si₁₆]. As for INH, it prefers to combine with Ti@Si₁₆ via the N atom of pyridine ring by forming a strongly polar N-Si bond. Differently, the interaction between Ti@Si₁₆ and the ASA, 5-Fu, and FPV drugs is dominated by the Van der Waals interaction. Our results reveal that DDP@[Ti@Si₁₆] possesses a moderate recovery time under body temperature, which benefits the desorption of DDP from Ti@Si₁₆. More importantly, the release of DDP drug from the Ti@Si₁₆ surface can be effectively controlled by exerting small orientation external electric fields on the DDP@[Ti@Si₁₆] complex. Therefore, this study demonstrates that Ti@Si₁₆ can serve as a promising drug carrier for DDP, and thus will further expand its practical applications in the biomedical field.

Structural and electronic properties of nanosize semiconductor HfSin0/-/2- (n = 6-16) material: a double-hybrid density functional theory investigation

Equilibrium geometries, thermodynamic stabilities, chemical reactivities, and electronic properties of neutral, mono-, and di-anionic Hf-doped silicon nanoclusters HfSi_n^0/-2- (n = 6-16) are calculated by employing an ABCluster global search technique combined with mPW2PLYP scheme. Based on the concordance between simulated and experimental PES, the true global minima are confirmed for n = 6, 9, and 12-16. Optimized geometries for neutral HfSi_n nanoclusters can be divided into three stages: first, Hf atom prefers locating on the surface site of the cluster for n = 6-9, which can be obtained by adding one, two, three, and four Si atoms to HfSi₅ tetragonal bipyramid, respectively (denoted as additive type); then, Hf atom is surrounded by Si atoms with half-cage configuration for n = 10-13; finally, Hf atom is encapsulated into Si cage pattern for n = 14-16. For mono-anions, it is from additive type (n = 6-11) to the cagelike configuration with Hf atom resided in silicon clusters (n = 12-16). For di-anions, it is additive type (n = 6-9) to the Hf-linked configuration (n = 10-11), and in the end to the Hf-encapsulated cagelike motif (n = 12-16). The thorough analysis of stability and chemical bonding revealed that the neutral HfSi₁₆ and di-anionic HfSi₁₅^2- are magic nanoclusters with good thermodynamic and chemical stability, which may make them as the most suitable building block for new functional materials. We suggest that the experimental PES of HfSi_n^- with n = 7, 8, 10, and 11 should be further examined due to the lack of comparably low electron binding energy peaks.

Study on Structural Evolution, Thermochemistry and Electron Affinity of Neutral, Mono- and Di-Anionic Zirconium-Doped Silicon Clusters ZrSin0/-/2- (n = 6-16)

We have carried out a global search of systematic isomers for the lowest energy of neutral and Zintl anionic Zr-doped Si clusters ZrSi_n^0/-/2- (n = 6–16) by employing the ABCluster global search method combined with the mPW2PLYP double-hybrid density functional. In terms of the evaluated energies, adiabatic electron affinities, vertical detachment energies, and agreement between simulated and experimental photoelectron spectroscopy, the true global minimal structures are confirmed. The results reveal that structural evolution patterns for neutral ZrSi_n clusters prefer the attaching type (n = 6–9) to the half-cage motif (n = 10–13), and finally to a Zr-encapsulated configuration with a Zr atom centered in a Si cage (n = 14–16). For Zintl mono- and di-anionic ZrSi_n^-/2-, their growth patterns adopt the attaching configuration (n = 6–11) to encapsulated shape (n = 12–16). The further analyses of stability and chemical bonding make it known that two extra electrons not only perfect the structure of ZrSi₁₅ but also improve its chemical and thermodynamic stability, making it the most suitable building block for novel multi-functional nanomaterials.