Structural evolution and bonding properties of Au2Sin−/0 (n = 1–7) clusters: Anion photoelectron spectroscopy and theoretical calculations

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.

Structural Determination and Bonding Characteristics of the Gas-Phase Ta2Si2̅ Anion and Its Neutral: Anion Photoelectron Spectroscopy and Theoretical Studies

The structures and bonding characteristics of Ta2Si2̅/0 clusters are investigated using anion photoelectron spectroscopy and quantum chemical calculations. The vertical detachment energy of the Ta2Si2̅ anion is measured to be 2.00 ± 0.08 eV using the 266 nm photon. It is found that the Ta2Si2̅ anion has three low-energy isomers with a C2v symmetric Ta-Ta dibridged structural framework, all of which contribute to the experimental photoelectron spectrum, while the Ta2Si2 neutral also has a C2v symmetric Ta-Ta dibridged structural framework. The charge-transfer from Ta atoms to Si atoms is discovered using atomic dipole moment corrected Hirshfeld analysis for the Ta2Si2̅ anion and Ta2Si2 neutral. Chemical bonding investigations show that both the Ta2Si2̅ anion and Ta2Si2 neutral have a strong covalent Ta-Ta bond, as well as σ and π double bonding patterns. Furthermore, the Ta atoms are linked together by a single 2c-2e Ta2 σ bond, whereas the Si atoms are linked together with the Ta atoms via four 2c-2e TaSi σ bonds, two 3c-2e TaSi2 σ bonds, one 4c-2e Ta2Si2 σ bond, and one 4c-2e Ta2Si2 π bond.

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.

Cr2 Gen - (n = 15-20) clusters with two Cr atoms exhibited antiferromagnetic coupling

In this work, we investigated the structural evolution, electronic and magnetic properties of Cr₂ Ge_n ^- clusters for n = 15-20 by using density functional theory (DFT) calculations. Low-energy structures for these clusters were fully searched through a self-developed genetic algorithm code combined with DFT calculations. The calculations show that all the two Cr atoms prefer to stay together to form a strong CrCr bond, which-except for size 20-is shorter than the nearest neighbor distance in Cr bulk. Sizes 15 and 16 adopt a wheel-like structure as the structural motif with the extra Ge atoms capped on the top, while larger sizes (n = 17-20) prefer fullerene-like Cr₂ @Ge₁₂ motifs. From the results of the average binding energies of Cr₂ Ge_n ^- , one can conclude that it is easier to form larger size clusters. In these lowest-lying isomers except for size 16, the two Cr atoms contribute opposite magnetic moments for the total magnetic moments of 1 μ_B , showing an antiferromagnetic state.

Structural evolution and electronic properties of neutral and anionic TiASil (A = Sc, Ti; l ≤ 12): relatively stable TiASi4 as a structural unit

Molecular orbitals (MO) and the HOMO–LUMO energy gaps (HLgs) of neutral TiASi4 clusters (A = Sc, Ti).

Anion photoelectron spectroscopy and density functional theory study of TM2Sin- (TM = V, Cr; n = 14-20) clusters

We investigated the structural evolution and electronic properties of medium-sized silicon cluster anions doped with two transition metal atoms, TM₂Si_n^- (TM = V, Cr; n = 14-20), by using mass-selective anion photoelectron spectroscopy combined with density functional theory (DFT) calculations. Putative ground state structures of these clusters were obtained by using a genetic algorithm coupled with the DFT calculations. It was found that the two TM atoms tend to form a TM-TM bond, which - except for V₂Si₁₉^- - is shorter than the nearest neighbour distance in the crystalline state of the respective metals. The V₂Si_n^- clusters with n = 14 to 17 exhibit structures based on a silicon hexagonal antiprism, while the larger ones exhibit more fullerene-like cage structures. Cr₂Si_n^- clusters follow the same trend, although with a silicon hexagonal prism structure for n = 14 and 15, and the transition to fullerene-like structures occurring at n = 17. Among these clusters, TM₂Si₁₈^- have the largest average binding energy and second order differences in energy, therefore the highest relative stability. All of the clusters possess total magnetic moment of 1 μB, but with very different contributions from the doped TM atoms. Especially in the Cr doped clusters there is a tendency towards an anitiferromagnetic arrangement of the magnetic moments of the two Cr atoms.

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.

Evolution of Vibrational Spectra in the Manganese-Silicon Clusters Mn2Sin, n = 10, 12, and 13, and Cationic [Mn2Si13]. J Phys Chem A 2022;126:1617-1626. [PMID: 35238570 PMCID: PMC9084549 DOI: 10.1021/acs.jpca.1c10027]

A comparison of DFT-computed and measured infrared spectra reveals the ground state structures of a series of gas-phase silicon clusters containing a common Mn₂ unit. Mn₂Si₁₂ and [Mn₂Si₁₃]⁺ are both axially symmetric, allowing for a clean separation of the vibrational modes into parallel (a₁) and perpendicular (e₁) components. Information about the Mn–Mn and Mn–Si bonding can be extracted by tracing the evolution of these modes as the cluster increases in size. In [Mn₂Si₁₃]⁺, where the antiprismatic core is capped on both hexagonal faces, a relatively simple spectrum emerges that reflects a pseudo-D_6d geometry. In cases where the cluster is more polar, either because there is no capping atom in the lower face (Mn₂Si₁₂) or the capping atom is present but displaced off the principal axis (Mn₂Si₁₃), the spectra include additional features derived from vibrational modes that are forbidden in the parent antiprism.

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.

Quantum chemistry calculations of the growth patterns, simulated photoelectron spectra, and electronic properties of LaASil (A = Sc, Y, La; l ≤ 10) compounds and their anions

The growth patterns, simulated photoelectron spectra, and electronic properties of LaASi_l (A = Sc, Y, and La; l ≤ 10) compounds and their anions were studied via quantum chemistry calculations using the Perdew-Burke-Ernzerhof (PBE) method and unprejudiced structural searching software ABCluster. The results revealed that the growth patterns of the most stable structures of neutral and anionic LaASi_l showed an adsorptive mode. The lowest-energy structures (LESs) of the LaASi_l (l ≤ 7) clusters were similar, except for those of anionic LaYSi₄^- and LaYSi₅^- and neutral LaScSi₇. Additionally, we investigated and calculated the photoelectron spectra, vertical detachment energies, adiabatic electron affinities, relative stability, charge transfer, magnetic moment, and chemical bond analysis of the LaASi_l ground-state structures. The La₂Si_l clusters exhibited higher stability than the LaYSi_l and LaScSi_l systems owing to their higher dissociation energies (DEs). The DEs of the LESs in the LaASi₃ molecule are higher than those of other clusters. Thus, the LaASi₃ cluster shows potential as a building framework for Si-based cluster materials with good stability. The natural population analysis data and chemical bond analysis results showed that the spd hybridization of the orbitals of the metal atoms in the LaASi_l system occurred. Except for the LaScSi₉ and LaScSi₁₀ clusters, the neutral LaASi_l compounds transform into the corresponding anions when an extra electron is accepted by the Si clusters.

Anion photoelectron spectroscopy and quantum chemistry calculations of TaSi16−/0 clusters: global minimum fullerene-like cage structure, bonding and superatom properties

TaSi₁₆⁻ has a fullerene-like cage structure, σ + π double delocalized bonding patterns, a superatom closed-shell electron configuration, and aromaticity.

Structural Evolution and Electronic Properties of TaSin-/0 (n = 2-15) Clusters: Size-Selected Anion Photoelectron Spectroscopy and Theoretical Calculations

The structural evolution and electronic properties of TaSi_n^-/0 (n = 2-15) clusters are explored using anion photoelectron spectroscopy accompanied by quantum chemical calculations. The Ta atom in TaSi_n^-/0 is inclined to interact with more Si atoms and has high coordination numbers. The theoretical calculations show that TaSi₂^-/0 have trianglur structures and TaSi₃^-/0 adopt pyramid structures, while the geometries of TaSi_n^-/0 (n = 4-7) are all exohedral structures dominated by bipyramid-based configurations with the Ta atom face-capping the Si_n motifs. TaSi₈^-/0 and TaSi_9-10^- have boat-shaped geometries, whereas TaSi_9-10 neutrals adopt bipyramid-based geometries instead of boat-shaped ones. TaSi₁₁^- and TaSi₁₂ are confirmed as the critical size of transiting from exohedral to endohedral structures for anionic and neutral clusters, respectively. TaSi_12-15^-/0 have pentagonal or hexagonal prism-based geometries. Natural population analysis shows that the electron transfers from Si_n skeletons to Ta atom. The second-order energy differences (Δ₂E) and incremental binding energy (ΔE^I) values exhibit strong odd-even alternations, suggesting that the TaSi_n-odd^-/0 clusters are more stable than the adjacent TaSi_n-even^-/0 ones, except that TaSi_12^-/0 are more stable than TaSi_11^-/0 and TaSi_13^-/0.

Au3Si4- and Au4Si4: Electronically Equivalent but Different Polarity Superatoms

A series of Au_xSi₄^- cluster anions (x = 1-4) were generated most abundantly by laser ablation of a Au₄Si alloy target. Photoelectron spectroscopy and density functional theory (DFT) calculation of Au_xSi₄^- (x = 1-4) revealed that Au₃Si₄^- can be viewed as an electronically closed superatom and is composed of a Si₄ unit whose three adjacent edges of a single facet are bridged by three Au atoms. Such phase-segregated structure is facilitated by aurophilic interaction between the three Au atoms and results in a large permanent dipole moment (4.43 D). DFT calculations on an electronically equivalent superatom Au₄Si₄ predicted a new structure in which the uncoordinated Si atom of Au₃Si₄^- is bonded by Au⁺. This Au₄Si₄ is much more stable than a cubic structure previously reported and has a large HOMO-LUMO gap (1.68 eV) and a small permanent dipole moment (0.41 D).

Structural evolution from exohedral to endohedral geometries, dynamical fluxionality, and structural forms of medium-sized anionic and neutral Au2Sin (n = 8–20) clusters

Au₂Si₈⁻, Au₂Si₉⁻, Au₂Si₁₃⁻, Au₂Si₁₅⁻, _Au2Si₁₇⁻ anions and Au₂Si₁₃, Au₂Si_{14, Au2}Si₁₇ neutrals show dynamical fluxionality. In addition, the odd-even alternations of chemical stabilities are observed in the anionic and neutral Au₂Si_n clusters.

Structures and bonding properties of CPt2 -/0 and CPt2H-/0: Anion photoelectron spectroscopy and quantum chemical calculations

We present a combined anion photoelectron spectroscopic and quantum chemical investigation on the structures and bonding properties of CPt₂ ^-/0 and CPt₂H^-/0. The experimental vertical detachment energies of CPt₂ ^- and CPt₂H^- are measured to be 1.91 ± 0.08 and 3.54 ± 0.08 eV, respectively. CPt₂ ^- is identified as a C_2v symmetric Pt-C-Pt bent structure, and CPt₂ has a D_∞h symmetric Pt-C-Pt linear structure. Both anionic and neutral CPt₂H adopt a Pt-C-Pt-H chain-shaped structure, in which the ∠PtCPt and ∠CPtH bond angles of CPt₂H^- are larger than those of CPt₂H. The Pt-C bonds in CPt₂ ^-/0 and CPt₂H^-/0 exhibit covalent double bonding characters. The Pt=C bonds are much stronger than the C-H bond that may explain why the C atom CPt₂H^-/0 prefers to form Pt=C bonds rather than C-H bonds. It may also explain why platinum can insert into the C-H bond to activate the C-H bond as reported in the literature.

Transition from exohedral to endohedral geometries of anionic and neutral B4Sin (n = 4-15) clusters: quantum chemical calculations

The growth patterns of anionic and neutral B4Sin (n = 4-15) clusters are investigated by using density functional theory (DFT) calculations combined with particle swarm optimization (CALYPSO) software. The geometries of anionic and neutral B4Sin clusters transform from exohedral to endohedral structures with the increasing cluster sizes. The B4Si14- anion size is critical for forming B4-endohedral structures for anionic clusters, while the B4Si15 neutral size is the threshold size for forming B4-endohedral structures for neutral clusters. Both anionic and neutral B4Sin (n = 4-15) clusters are primarily dominated by prism-based or bipyramid-based geometries. The global minima of anionic and neutral B4Sin clusters adopt different geometrical structures, except for anionic and neutral B4Si10. The binding energies, second-order energy differences, and incremental binding energies of B4Sin- clusters show an odd-even alternation with the growing number of Si atoms. The B atoms in B4Sin-/0 exhibit B-B single bonding and B[double bond, length as m-dash]B double bonding properties. The B atoms are found to carry more negative charges due to charge transfer from Sin frameworks to B atoms. Interestingly, the B4Si4- anion adopts a C2h symmetric bicapped tetragonal bipyramid with σ plus π double bonding characters and has the highest relative stability among the anionic clusters. The bonding interactions in B4Si4- are in the order of B-B > B-Si > Si-Si.

Structural exploration of AuxM− (M = Si, Ge, Sn; x = 9–12) clusters with a revised genetic algorithm

We used a revised genetic algorithm (GA) to explore the potential energy surface (PES) of Au_xM⁻ (x = 9–12; M = Si, Ge, Sn) clusters. The most interesting finding in the structural study of Au_xSi⁻ (x = 9–12) is the 3D (Au₉Si⁻ and Au₁₀Si⁻) → quasi-planar 2D (Au₁₁Si⁻ and Au₁₂Si⁻) structural evolution of the Si-doped clusters, which reflects the competition of Au–Au interactions (forming a 2D structure) and Au–Si interactions (forming a 3D structure). The Au_xM⁻ (x = 9–12; M = Ge, Sn) clusters have quasi-planar structures, which suggests a lower tendency of sp³ hybridization and a similarity of electronic structure for the Ge or Sn atom. Au₉Si⁻ and Au₁₀Si⁻ have a 3D structure, which can be viewed as being built from Au₈Si⁻ and Au₉Si⁻ with an extra Au atom bonded to a terminal gold atom, respectively. In contrast, the quasi-planar structures of Au_xM⁻ (x = 9–12; M = Ge, Sn) reflect the domination of the Au–Au interactions. Including the spin–orbit (SO) effects is very important to calculate the simulated spectrum (structural fingerprint information) in order to obtain quantitative agreement between theoretical and future experimental PES spectra.

We used a revised genetic algorithm (GA) to explore the potential energy surface (PES) of Au_xM⁻ (x = 9–12; M = Si, Ge, Sn) clusters.