Super Atomic Clusters: Design Rules and Potential for Building Blocks of Materials

Revisiting the trapping of noble gases (He-Kr) by the triatomic H3+ and Li3+ species: a density functional reactivity theory study

Small atomic clusters with exotic stability, bonding, aromaticity, and reactivity properties can be made use of for various purposes. In this work, we revisit the trapping of noble gas atoms (He-Kr) by the triatomic H₃⁺ and Li₃⁺ species by using some analytical tools from density functional theory, conceptual density functional theory, and the information-theoretic approach. Our results showcase that though similar in geometry, H₃⁺ and Li₃⁺ exhibit markedly different behavior in bonding, aromaticity, and reactivity properties after the addition of noble gas atoms. Moreover, the exchange-correlation interaction and steric effect are key energy components in stabilizing the clusters. This study also finds that the origin of the molecular stability of these species is due to the spatial delocalization of the electron density distribution. Our work provides an additional arsenal towards a better understanding of small atomic clusters capturing noble gases.

Molecular crystals vs. superatomic lattice: a case study with superalkali-superhalogen compounds

Using a first-principles approach, we study the assembly of atomically-precise cluster solids with atomic precision. The aims are to create binary assemblies of clusters through charge transfer between neutral molecular clusters, and employing intercluster electrostatic attraction as a driving force for co-assembly. We combined pairs of complementary clusters in which one cluster is electron-donating (superalkali) and the other is electron-accepting (superhalogen). From the analysis of the binding energy between superatomic counterparts, charge transfer, and the relative size of the clusters, we analyze the resulting structures as either molecular crystals or superatomic lattices. We demonstrate that the substitution of a single atom can result in minor changes to the crystal structure of the binary solids or entirely new packing structures. The [N₄Mg₆Li]⁺[AlCl₄]^-, [N₄Mg₆Na]⁺[AlCl₄]^-, [N₄Mg₆K]⁺[AlCl₄]^-, [N₄Mg₆Li]⁺[AlF₄]^-, [N₄Mg₆Na]⁺[AlF₄]^-, and [N₄Mg₆K]⁺[AlF₄]^- compounds all form the same close-packed superatomic lattice structure through halogen bonding, with subtle differences in the orientation of the superatoms. These salts may also form molecular crystals where clusters are held to one another by electrostatic interactions. Our results emphasize how the structure of superatomic solids can be tuned upon single atom substitution.

High-Stability Light-Element Magnetic Superatoms Determined by Hund's Rule

Achieving stable high-magnetism light-element structures at nanoscale is vital to the field of magnetism, which has traditionally been ruled by transition-metal elements with localized d or f electrons. By first-principles calculations, we show that superatoms made of pure earth-abundant light elements (i.e., boron and nitrogen) exhibit desired magnetic properties that rival those of rare-earth elements, and the magnetism is dictated entirely by Hund's maximum spin rule. Importantly, the chemical and structural stabilities of the superatoms are not jeopardized by its high spins and are in fact better than those of transition-metal-element-embedded clusters. Our work thus establishes the basic principles for designing novel light-element, high-stability, and high-moment magnetic superatoms.

Inverse Design of Nanoclusters for Light-Controlled CO2-HCOOH Interconversion

With global push of hydrogen economy, efficient scenarios for hydrogen storage, transportation, and generation are indispensable. Here we devise a strategy for controllable hydrogen fuel storage and retrieval via light-switched CO₂-to-HCOOH interconversion. To realize it, palladium sulfide nanocluster catalysts with multiple specific functionalities are directly searched by our home-developed inverse design approach based on genetic algorithm (IDOGA) and ab initio calculations. Over 500 low-energy Pd_xS_y (x + y ≤ 30) clusters are sieved through a multiobjective function combining stability, activity, optical absorption, and reduction capability of photocarriers. The structure-property relationships and key factors governing the trade-off among these stringent criteria are disclosed. Finally, 14 candidate Pd_xS_y clusters with proper sulfidation degree and high stability in an aqueous environment have been screened. Our IDOGA program provides a general approach for inverse search of nanoclusters with any designated elemental compositions and functionalities for any device applications.

The unique sandwich K6Be2B6H6 cluster with a real borozene B6H6 core

Theoretical evidence is reported for a boron-based K₆Be₂B₆H₆ sandwich cluster, showing a perfectly D _6h B₆H₆ ring, being capped by two tetrahedral K₃Be ligands. Due to the comfortable charge transfer, the sandwich is viable in [K₃Be]³⁺[B₆H₆]^6-[BeK₃]³⁺ ionic complex in nature. The [B₆H₆]^6- core with 6π aromaticity vividly imitates the benzene (C₆H₆), occurring as a real borozene. In contrast, the tetrahedral [K₃Be]³⁺ ligand is 2σ three-dimensional aromatic, acting as the simple superatom. Thus, this complex possesses a collectively three-fold 2σ/6π/2σ aromaticity. The interlaminar interaction is governed by the robust electrostatic attraction. The unique chemical bonding gives rise to interesting dynamic fluxionality.

Al13− and B@Al12− superatoms on a molecularly decorated substrate

Aluminum nanoclusters (Al_n NCs), particularly Al₁₃⁻ (n = 13), exhibit superatomic behavior with interplay between electron shell closure and geometrical packing in an anionic state. To fabricate superatom (SA) assemblies, substrates decorated with organic molecules can facilitate the optimization of cluster–surface interactions, because the molecularly local interactions for SAs govern the electronic properties via molecular complexation. In this study, Al_n NCs are soft-landed on organic substrates pre-deposited with n-type fullerene (C₆₀) and p-type hexa-tert-butyl-hexa-peri-hexabenzocoronene (HB-HBC, C₆₆H₆₆), and the electronic states of Al_n are characterized by X-ray photoelectron spectroscopy and chemical oxidative measurements. On the C₆₀ substrate, Al_n is fixed to be cationic but highly oxidative; however, on the HB-HBC substrate, they are stably fixed as anionic Al_n⁻ without any oxidations. The results reveal that the careful selection of organic molecules controls the design of assembled materials containing both Al₁₃⁻ and boron-doped B@Al₁₂⁻ SAs through optimizing the cluster–surface interactions.

Anionic aluminium clusters are promising candidates for the fabrication of superatom-assembled nanomaterials. Here, the authors report enhanced stability for Al₁₃⁻ and boron-doped B@Al₁₂⁻ on a molecularly decorated p-type organic substrate.

Designing Special Nonmetallic Superalkalis Based on a Cage-like Adamanzane Complexant

In this study, to examine the possibility of using cage-like complexants to design nonmetallic superalkalis, a series of X@3⁶adz (X = H, B, C, N, O, F, and Si) complexes have been constructed and investigated by embedding nonmetallic atoms into the 3⁶adamanzane (3⁶adz) complexant. Although X atoms possess very high ionization energies, these resulting X@3⁶adz complexes possess low adiabatic ionization energies (AIEs) of 0.78–5.28 eV. In particular, the adiabatic ionization energies (AIEs) of X@3⁶adz (X = H, B, C, N, and Si) are even lower than the ionization energy (3.89 eV) of Cs atoms, and thus, can be classified as novel nonmetallic superalkalis. Moreover, due to the existence of diffuse excess electrons in B@3⁶adz, this complex not only possesses pretty low AIE of 2.16 eV but also exhibits a remarkably large first hyperpolarizability (β₀) of 1.35 × 10⁶ au, indicating that it can also be considered as a new kind of nonlinear optical molecule. As a result, this study provides an effective approach to achieve new metal-free species with an excellent reducing capability by utilizing the cage-like organic complexants as building blocks.

The wavelength-dependent non-linear absorption and refraction of Au25 and Au38 monolayer-protected clusters

In the past decade, the structural and electronic properties of monolayer-protected metal clusters, which can be produced size-selected in macroscopic amounts, have received a lot of attention. Their great potential for optical applications has been identified. In the high intensity regime, monolayer-protected metal clusters show pronounced nonlinear absorption and refraction. Naturally, these phenomena are wavelength-dependent, however, such dependence is largely unexplored. Here, we quantify the wavelength-dependent non-linear optical absorption and refraction cross sections of atomically precise Au₂₅(DDT)₁₈ and Au₃₈(DDT)₂₄ clusters, using the z-scan technique in combination with a tunable nanosecond laser source. Qualitatively different non-linear optical phenomena were found to take place at different excitation wavelengths (two-photon and excited-state absorption, intensity saturation and non-linear refraction). Both clusters have high nonlinear absorption cross sections at 532 nm, and present a (local) maximum at 640 nm, together with a maximum in the absorption saturation. The nonlinear refraction is always negative for Au₂₅(DDT)₁₈, while it changes sign for Au₃₈(DDT)₂₄. Depending on the wavelength, the underlying mechanism of the nonlinear absorption effects is two-photon absorption or excited state absorption. The obtained very high nonlinear cross sections, on the order of 10⁷-10⁹ GM, demonstrate the great potential of those clusters as nonlinear absorption or refraction materials in optical applications.

Tri- and Tetra-superatomic Molecules in Ligand-Protected Face-Fused Icosahedral (M@Au12)n (M = Au, Pt, Ir, and Os, and n = 3 and 4) Clusters

Cluster assembling has been one of the hottest topics in nanochemistry. In certain ligand-protected gold clusters, bi-icosahedral cores assembled from Au₁₃ superatoms were found to be analogues of diatomic molecules F₂, N₂, and singlet O₂, respectively, in electronic shells, depending upon the super valence bond (SVB) model. However, challenges still remain for extending the scale in cluster assembling via the SVB model. In this work, ligand-protected tri- and tetra-superatomic clusters composed of icosahedral M@Au₁₂ (M = Au, Pt, Ir, and Os) units are theoretically predicted. These clusters are stable with reasonable highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps and proven to be analogues of simple triatomic (Cl₃^-, OCl₂, O₃, and CO₂) and tetra-atomic (N≡C-C≡N, and Cl-C≡C-Cl) molecules in both geometric and electronic structures. Moreover, a stable cluster-assembling gold nanowire is predicted following the same rules. This work provides effective electronic rules for cluster assembling on a larger scale and gives references for their experimental synthesis.

Relativistic Effects in Platinum Nanocluster Catalysis: A Statistical Ensemble-Based Analysis

Nanoclusters are materials of paramount catalytic importance. Among various unique properties featured by nanoclusters, a pronounced relativistic effect can be a decisive parameter in governing their catalytic activity. A concise study delineating the role of relativistic effects in nanocluster catalysis is carried by investigating the oxygen reduction reaction (ORR) activity of a Pt₇ subnanometer cluster. Global optimization analysis shows the critical role of spin-orbit coupling (SOC) in regulating the relative stability between structural isomers of the cluster. An overall improved ORR adsorption energetics and differently scaled adsorption-induced structural changes are identified with SOC compared to a non-SOC scenario. Ab initio atomistic thermodynamics analysis predicted nearly identical phase diagrams with significant structural differences for high coverage oxygenated clusters under realistic conditions. Though inclusion of SOC does not bring about drastic changes in the overall catalytic activity of the cluster, it is having a crucial role in governing the rate-determining step, transition-state configuration, and energetics of elementary reaction pathways. Furthermore, a statistical ensemble-based approach illustrates the strong contribution of low-energy local minimum structural isomers to the total ORR activity, which is significantly scaled up along the activity improving direction within the SOC framework. The study provides critical insights toward the importance of relativistic effects in determining various catalytic activity relevant features of nanoclusters.

Photoelectron Spectroscopy and Density Functional Investigation of the Structural Evolution, Electronic, and Magnetic Properties of CrSin- (n = 14-18) Clusters

CrSi_n^- (n = 14-18) cluster anions have been investigated by a combination of photoelectron spectroscopy (PES) and first-principles calculations. The lowest-lying structures of the clusters have been determined by a global minimum search based on the genetic algorithm, combined with density functional theory (DFT) calculations. The simulated PES spectra of the lowest-energy isomers are in agreement with the experimental results, which gives strong evidence that the correct structures have been found. While sizes n = 14 and n = 15 prefer cage-like structures based on multi-center bonding within the cage, the larger sizes adopt structures based on fullerene-type cages around the Cr atom, with the additional atoms attached to the cage surface. A Hirshfeld analysis shows that the Cr atoms act as electron donors in all clusters, thus enhancing the electron count in the cage. It also reveals that the magnetic moment of 1μ_B shown by all clusters is mainly contributed by the Cr atom. One interesting exception is size 17, where the Cr atom contributes a small moment antiparallel to that of the silicon cage.

Mapping the Finite-Temperature Behavior of Conformations to Their Potential Energy Barriers: Case Studies on Si6B and Si5B Clusters

Dynamical simulations of molecules and materials have been the route to understand the rearrangement of atoms within them at different temperatures. Born-Oppenheimer molecular dynamical simulations have further helped to comprehend the reaction dynamics at various finite temperatures. We take a case study of Si₆B and Si₅B clusters and demonstrate that their finite-temperature behavior is rather mapped to the potential energy surface. The study further brings forth the fact that an accurate description of the dynamics is rather coupled with the accuracy of the method in defining the potential energy surface. A more precise potential energy surface generated through the coupled cluster method is finally used to identify the most accurate description of the potential energy surface and the interconnected finite-temperature behavior.

SbCl4: An Exceptional Superhalogen as the Building Block of a Mixed Valence Supercrystal with Unconventional Ferroelectricity

Superhalogens are nanoclusters with high electron affinities, exhibiting behavior similar to that of halogens. Their dimerization yields nonpolar symmetrical clusters, akin to diatomic halogen molecules, and they are unstable in the condensed phase in the absence of charge-compensating cations. Herein, we provide ab initio evidence that SbCl₄ superhalogen is an exception: its dimerization yields a polar cluster that can be viewed as a quasi-bonded [SbCl₅]^δ- and [SbCl₃]^δ+ Lewis acid-base cluster. The symmetry breaking arises from the valence stratification of Sb into Sb⁵⁺ and Sb³⁺ as well as their lone pair electrons. When assembled, SbCl₄ clusters form a supercrystal that is thermodynamically stable up to 600 K, with the unique bonding feature of Sb₂Cl₈ prevailing in the bulk phase. Combination of mixed valence and lone pair electrons leads to electric polarizations along all directions, generating a type of unconventional multimode ferroelectricity in which three different modes of ferroelectricity with distinct magnitudes and Curie temperature are revealed.

Metallo-boranes: a class of unconventional superhalogens defying electron counting rules

Superhalogens are a class of highly electronegative atomic clusters whose electron affinities exceed those of halogens. Due to their potential for promoting unusual reactions and role as weakly coordinating anions as well as building blocks of bulk materials, there has been considerable interest in their design and synthesis. Conventional superhalogens are composed of a metal atom surrounded by halogen atoms. Their large electron affinities are due to the fact that the added electron is distributed over all the halogen atoms, reducing electron-electron repulsion. Here, using density functional theory with a hybrid exchange-correlation functional, we show that a new class of superhalogens can be developed by doping closo-boranes (e.g., B₁₂H₁₂) with selected metal atoms such as Zn and Al as well as by replacing a B atom with Be or C. Strikingly, these clusters defy electron counting rules. For example, according to the Wade-Mingos rule, Zn(B₁₂H₁₂) and Al(BeB₁₁H₁₂) are closed-shell systems that should be chemically inert and, hence, should have very small electron affinities. Similarly, Zn(B₁₂H₁₁), Al(B₁₂H₁₂), and Zn(CB₁₁H₁₂), with one electron more than needed for electronic shell closure, should behave like superalkalis. Yet, all these clusters are superhalogens. This unexpected behavior originates from an entirely different mechanism where the added electron resides on the doped metal atom that is positively charged due to electron transfer.

Antiperovskite Electrolytes for Solid-State Batteries

Solid-state batteries have fascinated the research community over the past decade, largely due to their improved safety properties and potential for high-energy density. Searching for fast ion conductors with sufficient electrochemical and chemical stabilities is at the heart of solid-state battery research and applications. Recently, significant progress has been made in solid-state electrolyte development. Sulfide-, oxide-, and halide-based electrolytes have been able to achieve high ionic conductivities of more than 10^-3 S/cm at room temperature, which are comparable to liquid-based electrolytes. However, their stability toward Li metal anodes poses significant challenges for these electrolytes. The existence of non-Li cations that can be reduced by Li metal in these electrolytes hinders the application of Li anode and therefore poses an obstacle toward achieving high-energy density. The finding of antiperovskites as ionic conductors in recent years has demonstrated a new and exciting solution. These materials, mainly constructed from Li (or Na), O, and Cl (or Br), are lightweight and electrochemically stable toward metallic Li and possess promising ionic conductivity. Because of the structural flexibility and tunability, antiperovskite electrolytes are excellent candidates for solid-state battery applications, and researchers are still exploring the relationship between their structure and ion diffusion behavior. Herein, the recent progress of antiperovskites for solid-state batteries is reviewed, and the strategies to tune the ionic conductivity by structural manipulation are summarized. Major challenges and future directions are discussed to facilitate the development of antiperovskite-based solid-state batteries.

Automatic structural elucidation of vacancies in materials by active learning

The artificial intelligence method based on active learning for the automatic structural elucidation of vacancies in materials. This is implemented in the quantum machine learning software/agent for material design and discovery (QMLMaterial).

Benzyl-rich ligand engineering of the photostability of atomically precise gold nanoclusters

A series of [core+exo]-type Au8 nanoclusters (NCs) bearing two benzyl-rich ligands on the exo gold atoms were synthesized, which exhibit significant photostability and chemical stability. Furthermore, the benzyl-rich ligands enhance...

Dimerization of sub-nanoscale molecular clusters affords broadly tuneable viscoelasticity above the glass transition temperature

Materials with promising mechanical performance generally demonstrate requirements for the critical sizes of their key building units, e.g. entanglements and crystal grains. Herein, only with van der Waals interaction, viscoelasticity with broad tunability has been facilely achieved below the critical size limits: the dimers of ∼1 nm polyhedral oligomeric silsesquioxane (POSS) with M_w < 4 kD and size < 5 nm, which demonstrate distinct material physics compared to that of polymer nanocomposites of POSS. The dimeric POSSs are confirmed by scattering and calorimetrical measurements to be intrinsic glassy materials with glass transition temperatures (T_gs) lower than room temperature. From rheological studies, their viscoelasticity can be broadly tuned through the simple tailoring of the dimer linker structures above their T_g. In dimer bulks, each POSS cluster is spatially confined by the POSSs from other dimers and therefore, the correlation of the dynamics of the two linked POSS clusters, which, as indicated by dynamics analysis, is regulated by the length and flexibilities of linkers, contributes to the caging dynamics of POSS confined by their neighbours and the resulting unique viscoelasticity. Our discoveries update the understanding of the structural origin of viscoelasticity and open avenues to fabricate structural materials from the design of sub-nanoscale building blocks.

The critical size limit for general structural material design is challenged in the dimers of sub-nm molecular clusters that possess small sizes (<5 nm) and broadly tunable viscoelasticity.

Sn368‒: A 2.7 nm Naked Aromatic Tin Rod

In this work, we synthesize naked tin cluster anion Sn368‒, representing the first example of pure Sn nanowire assembled through oxidative coupling reactions of a super atomic cluster Sn94-. Theoretical...

The mystery of Ph3PS revealed in magic-size Ag–S cluster nucleation

PPh3S was employed to direct the regulation of {Ag32S3} cluster by slowing down the kinetic process of nucleation. The process that Agn(CCBut)m and traces of water induces breakage of PS from [Ag2(Ph3PS)4]2+ to generate {Ag32S3} was established.

High electron affinity triggered by lithium coordination: quasi-chalcogen properties of Li2Sn8Be

This work puts forward an unusual but rational strategy to design superatoms mimicking the properties of group VIA elements. A stable dianion with closo-configuration, namely Li2Sn8Be2−, has been obtained by...

Electron counting in cationic and anionic silver clusters doped with a 3d transition-metal atom: endo- vs. exohedral geometry

Cationic and anionic AgNM+/− (M = Sc–Ni) clusters are explored to examine the electron-counting rule. Among 18-valence-electron clusters, endohedrally doped ones are stable due to superatomic electron-shell closure involving delocalized 3d electrons.

On the Precise and Continuous Regulation of the Superatomic and Spectroscopic Behaviors of the Quasi-Cubic W4C4 Cluster by the Oriented External Electric Field

Designing and realizing novel superatoms with controllable and tunable electronic properties is vital for their potential applications in cluster-assembly nanomaterials. Here, we investigated the effect of the oriented external electric field (OEEF) on the geometric and electronic structures as well as the spectroscopic properties of the quasi-cubic W₄C₄ cluster by utilizing the density functional theory (DFT) calculations. Compared with traditional models, the OEEF was observed to hold the special capability in continuously and precisely modulating the electronic properties of W₄C₄, that is, remarkably increasing its electron affinity (EA) (1.58 eV) to 5.61 eV under the 0.040 au OEEF (larger than any halogen atoms in the periodic table), which possesses the superhalogen behavior. Furthermore, the downward movement of the lowest unoccupied molecular orbital level of the cluster accompanied by the enhancement of the OEEF intensity was demonstrated to be the origin of the EA increment. Additionally, the photoelectron spectra (PES) of W₄C₄^- were also simulated under different OEEF intensities, where the PES peaks move to a higher energy area following the enhancement of the OEEF strength, exhibiting the blue-shift behavior. These findings observed here open a new avenue in conveniently and precisely adjusting the electronic properties of clusters, which will be beneficial for the rational design of superatoms or superatom-assembled nanomaterials under the external field.

Ground and Electronically Excited States of Main-Group-Metal-Doped B20 Double Rings

Ab initio coupled-cluster, electron propagator, and Møller-Plesset second-order perturbation theory calculations are utilized to analyze the low-lying electronic states of several metal-doped B₂₀. In the ground state, the presently focused AB₂₀/EB₂₀ (A = Li, Na, and K; E = Mg and Ca) consist of charge-separated A⁺B₂₀^-/E²⁺B₂₀^2- frameworks. The excited electronic states of AB₂₀ and EB₂₀⁺ were analyzed by computing the vertical electron attachment energies (VEAEs) of AB₂₀⁺ and EB₂₀²⁺. In several excited states, the radical electron is predominantly localized on the B₂₀ frames, which are counterparts of the low-lying states of bare B₂₀^-. A variety of basis sets were tested on obtaining VEAEs, and the aug-cc-pVDZ/_A,E d-aug-cc-pVDZ/_B combination provided the best accuracy-efficiency compromise on them. Furthermore, this work analyzes the Rydberg-like excited states of AB₂₀ and EB₂₀⁺ and will serve as a guide for future studies on similar metal-doped boron systems.

Superatomic Chelates: The Cases of Metal Aza-Crown Ethers and Cryptands

Li, Na, and Mg⁺-coordinated hexaaza-18-crown-6 ([18]aneN₆) and 1,4,7-triazacyclononane ([9]aneN₃), Li[1.1.1]cryptand, and Na[2.2.2]cryptand species possess a diffuse electron in a quasispherical s-type orbital. They populate expanded p-, d-, f-, and g-shape orbitals in low-lying excited states and hence are identified as "superatoms". By means of quantum calculations, their superatomic shell models are revealed. The observed orbital series of M([9]aneN₃)₂ and M[18]aneN₆ (M = Li, Na, Mg⁺) are identical to the 1s, 1p, 1d, 1f, 2s, and 2p. The electronic spectra of Li[1.1.1]cryptand and Na[2.2.2]cryptand were analyzed up to the 1f¹ configuration, and their transitions were found to occur at lower energies compared to their aza-crown ethers. The introduced superatomic shell models in this work closely resemble the Aufbau principle of "solvated electrons precursors". All reported alkali metal complexes bear lower ionization potentials than any atom in the periodic table; thus, they can also be recognized as "superalkalis".

Unusual structural transformation and luminescence response of magic-size silver(I) chalcogenide clusters via ligand-exchange

Structural transformations of nanoclusters provide a platform to tune their properties and understand the fundamental science due to their intimate structure-property correlation. Here, we present an alkynyl ligand-exchange induced growth of atomically precise silver(I) clusters, which are particularly of interest because of their luminescence response at room temperature. SCXRD and UV-vis map out the growth steps of the cluster from [Ag₃₂S₃(CCBu^t)₂₃]³⁺ featuring a pseudo-D_3h concave Ag₃₂S₃ to [Ag₄₅S₆(CCPhBr)₃₂]⁺ with a pseudo-O_h core-shell Ag₉S₆@Ag₂₄@Ag₁₂, which is driven by a thermodynamic route under the disruption of ligands. To our knowledge, the findings in this work establish the first example of ligand-exchange as a versatile tool for tuning the size and luminescence of semiconductor silver(I) clusters.

Cluster Assembled Silicon-Lithium Nanostructures: A Nanowire Confined Inside a Carbon Nanotube

We computationally explore an alternative to stabilize one-dimensional (1D) silicon-lithium nanowires (NWs). The Li₁₂Si₉ Zintl phase exhibits the NW [Li6Si5]∞1, combined with Y-shaped Si₄ structures. Interestingly, this NW could be assembled from the stacking of the Li₆Si₅ aromatic cluster. The [Li6Si5]∞1@CNT nanocomposite has been investigated with density functional theory (DFT), including molecular dynamics simulations and electronic structure calculations. We found that van der Waals interaction between Li’s and CNT’s walls is relevant for stabilizing this hybrid nanocomposite. This work suggests that nanostructured confinement (within CNTs) may be an alternative to stabilize this free NW, cleaning its properties regarding Li₁₂Si₉ solid phase, i.e., metallic character, concerning the perturbation provided by their environment in the Li₁₂Si₇ compound.

Multi-swarm UPSO algorithm based on seed strategy for atomic clusters structure optimization

Particle Swarm Optimization (PSO) algorithm is prone to get trapped in local optima and insufficient information exchange among particles. To solve this problem, this paper proposes a Multi-swarm Unified Particle Swarm Optimization algorithm based on Seed Strategy (SS-DMS-UPSO) to optimize the atomic clusters structure. In this algorithm, the population is divided into some sub-populations evolving randomly and evenly, and each sub-population uses UPSO algorithm with different unification factors to evolve independently in parallel. After a certain number of independent evolution, the particles of all sub-populations are merged into a new population, and the population is again randomly divided into average sub-populations. Iterate the algorithm repeatedly in this way. And finally the global best particle can be obtained. The experimental results show that the SS-DMS-UPSO algorithm can search for the optimal structure or extremely similar optimal structure for atomic clusters with atomic numbers between 2 and 31. For atomic clusters with atomic numbers between 32 and 35, the algorithm can find its approximate optimal structure. Compared with other algorithms, the difference between the lowest energy value and the ideal energy value obtained by the SS-DMS-UPSO algorithm is much smaller. It means that its optimal structure of the atomic clusters is closer to the stable structure, and the algorithm is more stable, which proves the effectiveness of the SS-DMS-UPSO algorithm.

Anion-Anion Chemistry with Mass-Selected Molecular Fragments on Surfaces

While reactions between ions and neutral molecules in the gas phase have been studied extensively, reactions between molecular ions of same polarity remain relatively unexplored. Herein we show that reactions between fragment ions generated in the gas phase and molecular ions of the same polarity are possible by soft-landing of both reagents on surfaces. The reactive [B₁₂ I₁₁ ]^1- anion was deposited on a surface layer built up by landing the generally unreactive [B₁₂ I₁₂ ]^2- . Ex-situ analysis of the generated material shows that [B₂₄ I₂₃ ]^3- was formed. A computational study shows that the product is metastable in the gas phase, but a charge-balanced environment of a grounded surface may stabilize the triply charged product, as suggested by model calculations. This opens new opportunities for the generation of highly charged clusters using unconventional building blocks from the gas phase.

Prediction of an Al4C4 superatom organic framework (SOF) material based on the superatom network model

Metal organic framework (MOF) materials have attracted significant attention due to their wide potential applications, but it is still a challenge to design MOFs with advanced properties by exploring novel metal nodes. In this study, a kind of superatom organic framework (SOF) material is proposed based on the superatom network (SAN) model. Tetrahedron Al₄ superatom unit is used as nodes in the MOF structure, and linear -CC- ligands are chosen as linkers. Localized chemical bonding analysis and nucleus-independent chemical shift (NICS) scan confirm that the Al₄ core keeps the superatom electronic shell in the SOF structure. Further calculations demonstrate that this Al₄C₄ crystal has high dynamic and thermal stabilities, with an indirect semiconductor band gap of 2.57 eV. Analysis of its optical properties indicates its potential applications as an optoelectronic device. This novel kind of SOF material has both porous framework as traditional MOFs and superatomic character in its nodes, indicating its unique potential properties. Our work would provide a new way for designing functional MOF materials.

Density functional theory studies of boron clusters with exotic properties in bonding, aromaticity and reactivity

Atomic clusters are unique in many perspectives because of their size and structure features and are continuously being applied for different purposes. To unveil their unconventional properties, in this work, using neutral tetraboron clusters as illustrative examples, we study their exotic behaviors in bonding, aromaticity, and reactivity. We show that both double and triple bonds can be formed, ring current patterns can be totally different, and both electrophilic and nucleophilic reactivities can coexist simultaneously. These features are often in contrast with our conventional chemical wisdom and could enrich the possibility for their potential applications. The methodologies employed in this work can be readily applied to other systems. Our studies should help us better appreciate atomic clusters with many atypical properties and henceforth yield novel applications.

Prediction of beryllium clusters (Ben; n = 3-25) from first principles

Evolutionary searches using the USPEX method (Universal Structure Predictor: Evolutionary Xtallography) combined with density functional theory (DFT) calculations were performed to obtain the global minimum structures of beryllium (Be_n, n = 3-25) clusters. The thermodynamic stability, optoelectronic and photocatalytic properties as well as the nature of bonding are considered for the most stable clusters. It is found that the cluster with n = 15 is the transition point at which the configurations change from 3D hollow cages to filled cage structures (with an interior atom appearing in the structure). All the ground state structures are energetically favorable with negative binding energies, suggesting good synthetic feasibility for these structures. The calculated relative stabilities and electronic structure show that the Be₄, Be₁₀ and, Be₁₇ clusters are the most stable structures and can be considered as superatoms. The electron configurations of Be₄, Be₁₀ and Be₁₇ clusters with 8, 20 and 34 electrons are identified as 1S² 1P⁶, 1S² 1P⁶ 1D¹⁰ 2S², 1S² 1P⁶ 1D¹⁰ 2S² 1F¹⁴, respectively. Theoretical simulations determined that all the ground state structures exhibit excellent thermal stability, where the upper-limit temperature that the structures can tolerate is 900 K. During AIMD simulation of O₂ adsorption onto the Be₁₇ cluster an interesting phenomenon was happening in which the pristine Be₁₇ cluster becomes a new stable Be₁₇O₁₆ cluster. Based on ELF (electron localization function) analysis, it can be concluded that the Be-Be bonds in the small clusters are primarily of van der Waals type, while for the larger clusters, the bonds are of metallic nature. The Be_n clusters show very strong absorption in the UV and visible regions with absorption coefficients larger than 10⁵ cm^-1, which suggests a wide range of potential advanced optoelectronics applications. The Be₁₇ cluster has a suitable band alignment in the visible-light excitation region which will produce enhanced photocatalytic activities (making it a promising material for water splitting).

Designing an alkali-metal-like superatom Ca3B for ambient nitrogen reduction to ammonia

Converting earth-abundant nitrogen (N₂) gas into ammonia (NH₃) under mild conditions is one of the most important issues and a long-standing challenge in chemistry. Herein, a new superatom Ca₃B was theoretically designed and characterized to reveal its catalytic performance in converting N₂ into NH₃ by means of density functional theory (DFT) computations. The alkali-metal-like identity of this cluster is verified by its lower vertical ionization energy (VIE, 4.29 eV) than that of potassium (4.34 eV), while its high stability was guaranteed by the large HOMO-LUMO gap and binding energy per atom (E_b). More importantly, this well-designed superatom possesses unique geometric and electronic features, which can fully activate N₂via a "double-electron transfer" mechanism, and then convert the activated N₂ into NH₃ through a distal reaction pathway with a small energy barrier of 0.71 eV. It is optimistically hoped that this work could intrigue more endeavors to design specific superatoms as excellent catalysts for the chemical adsorption and reduction of N₂ to NH₃.

Realization of the Zn3+ oxidation state

Due to unfilled d-shells, transition metal atoms exhibit multiple oxidation states and rich chemistry. While zinc is often classified as a transition metal, electrons in its filled 3d¹⁰ shell do not participate in chemical reactions; hence, its oxidation state is +2. Using calculations based on density functional theory, we show that the chemistry of zinc can fundamentally change when it is allowed to interact with highly stable super-electrophilic trianions, namely, BeB₁₁(CN)₁₂^3- and BeB₂₃(CN)₂₂^3-, which lie 15.85 eV and 18.49 eV lower in energy than their respective neutral states. The fact that Zn exists in +3 oxidation states while interacting with these moieties is evidenced from its large binding energies of 6.33 and 7.04 eV with BeB₁₁(CN)₁₂^3- and BeB₂₃(CN)₂₂^3-, respectively, and from a comprehensive analysis of its bonding characteristics, charge density distribution, electron localization function, molecular orbitals and energy decomposition, all showing a strong involvement of its 3d electrons in chemical bonding. The replacement of CN with BO is found to increase the zinc binding energy even further.

A Simple Entropic-Driving Separation Procedure of Low-Size Silver Clusters, Through Interaction with DNA

Synthesis and purification of metal clusters without strong binding agents by wet chemical methods are very attractive for their potential applications in many research areas. However, especially challenging is the separation of uncharged clusters with only a few number of atoms, which renders the usual techniques very difficult to apply. Herein, we report the first efficient separation of Ag2 and Ag3 clusters using the different entropic driving forces when such clusters interact with DNA, into which Ag3 selectively intercalates. After sequential dialysis of the samples and denaturalizing the DNA-Ag3 complex, pure Ag2 can be found in the dialysate after extensive dialysis. Free Ag3 is recovered after DNA denaturation.

Search for Global Minimum Structures of P 2 n + 1 + (n = 1-15) Using xTB-Based Basin-Hopping Algorithm

A new program for searching global minimum structures of atomic clusters using basin-hopping algorithm based on the xTB method was developed here. The program can be performed with a much higher speed than its replacement directly based on DFT methods. Considering the structural varieties and complexities in finding their global minimum structures, phosphorus cluster cations were studied by the program. The global minimum structures of cationic P2n+1+ (n = 1–15) clusters are determined through the unbiased structure searching method. In the last step, further DFT optimization was performed for the selected isomers. For P2n+1+ (n = 1–4, 7), the found global minimum structures are in consistent with the ones previously reported; while for P2n+1+ (n = 5, 6, 8–12), newly found isomers are more energy-favorable than those previously reported. And those for P2n+1+ (n = 13–15) are reported here for the first time. Among them, the most stable isomers of P2n+1+ (n = 4–6, 9) are characterized by their C_3v, C_s, C_2v and C_s symmetry, in turn. But those of P2n+1+ (n = 7, 8, 10–12), no symmetry has been identified. The most stable isomers of P29+ and P31+ are characterized by single P-P bonds bridging units inside the clusters. Further analysis shows that the pnicogen bonds play an important role in the stabilization of these clusters. These results show that the new developed program is effective and robust in searching global minimum structures for atom clusters, and it also provides new insights into the role of pnicogen bonds in phosphorus clusters.

Small lithium-chloride clusters: Superalkalis, superhalogens, supersalts and nanocrystals

In the present paper, the results of the theoretical investigation of the small lithium-chloride clusters are reported. The geometrical structures, electronic and thermodynamic stability of superalkalis, superhalogens, and their single and double charged ions are obtained using efficient and accurate quantum chemistry methods. Further, low-lying isomers of the Li_n Cl_n ( n = 2 - 5 ) clusters and their stability parameters are calculated. Two ways of formation of the Li_n Cl_n clusters, polymerization of LiCl fragments and combination of superalkalis and superhalogen clusters, are compared. By examination the lattice energy and the average Li-Cl bond length in rectangular Li_n Cl_n ( n ≤ 60 ) clusters, it was concluded that already 50 LiCl are enough to mostly resembles the structure and stability of the bulk LiCl.