Structures and magnetic properties of CrSin− (n = 3–12) clusters: Photoelectron spectroscopy and density functional 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.

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.

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.

Structural Evolution and Bonding Properties of Cr2Sin- (n = 1-12) Clusters: Mass-Selected Anion Photoelectron Spectroscopy and Theoretical Calculations

We investigated the structural characteristics and bonding properties of Cr₂Si_n^- (n = 1-12) clusters by using anion photoelectron spectroscopy combined with density functional theory calculations. The experimental and theoretical results reveal that Cr atoms of the most stable structures of Cr₂Si_n^- clusters with n < 8 are located at the surface, while the most stable structures of Cr₂Si_n^- clusters with n ≥ 8 have one Cr encapsulated in the cage consisting of the other Cr atom and the Si atoms. The Cr-Cr interaction in the most stable structures of Cr₂Si_n^- clusters is strong, except that the Cr-Cr interaction in the lowest lying isomer of the Cr₂Si₅^- cluster is weak. The structure of Cr₂Si₆^- can be viewed as the Cr₂ surrounded by a chair-shaped silicon six-membered ring with the C_2h symmetry. Cr₂Si₁₂^- has a C_6v symmetric antihexagonal prism structure with two Cr atoms located at the center and the surface of the Si₁₂ cage, respectively. The magnetic moments of Cr₂Si_n^- are 1 μB except that the magnetic moment of Cr₂Si₅^- is 9 μB.

Structural and Electronic Properties of LaSin-/0 (n = 2-6) Clusters: Anion Photoelectron Spectroscopy and Density Functional Calculations

The structures and electronic properties of LaSi_n^- (n = 2-6) anions and their neutral counterparts were investigated by anion photoelectron spectroscopy and theoretical calculations. The vertical detachment energies of the most stable structures of LaSi_n^- (n = 2-6) were measured to be 1.28, 1.58, 2.30, 2.05, and 2.91 eV, respectively. The lowest-energy isomer of LaSi₂^- is an isosceles triangle with a C_2v symmetry. For LaSi_3-6^- clusters, the most stable isomers are polyhedrons with La atom face-capping the Si_n frameworks. The lowest-energy structures of neutral LaSi_2,4,5 clusters are similar to their anionic counterparts. The most stable isomer of neutral LaSi₃ is a planar structure with C_2v symmetry, which is different from the triangular pyramid structure of LaSi₃^- anion. The lowest-energy isomer of LaSi₆^- is a C_5v symmetric pentagonal bipyramid structure, while for neutral LaSi₆ cluster, the C_5v structure is not the most stable one. The natural population analysis showed that there is electron transfer from La atoms to Si atoms in LaSi_n^-/0 (n = 2-6). The ZZ tensor component in isochemical shielding surfaces and the anisotropy of the induced current density analyses indicate that the most stable isomer of LaSi₆^- has 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.

Dynamical fluxionality, multiplicity of structural forms, and electronic properties of the B3Si11 cluster: anion photoelectron spectroscopy and theoretical calculations

The geometrical structures and electronic properties of anionic, neutral, and cationic B₃Si₁₁ clusters were investigated by performing ab initio calculations combined with size-selected anion photoelectron spectroscopy. The experimental photoelectron spectrum of the B₃Si₁₁^- anion is reasonably reproduced by theoretical simulations of two competing isomers. The global minimum of the B₃Si₁₁^- anion is formed by the fusion of a B₃Si₇ bicapped tetragonal antiprism to a B₃Si₄ pentagonal bipyramid by sharing a B₃ triangle, while that of neutral B₃Si₁₁ has a B₃-endohedral sandwich structure composed of a Si₅ five-membered ring and a Si₆ six-membered ring, and that of the B₃Si₁₁⁺ cation adopts a Si₁₁ tricapped tetragonal antiprism with three face-capping B atoms. It is interesting that a Si₅ five-membered ring and a Si₆ six-membered ring are stabilized by three B atoms in B₃Si₁₁. The three B atoms tend to bond with each other to form a B₃ triangle with stronger B-B bonds than B-Si bonds. Moreover, neutral B₃Si₁₁ exhibits σ + π double delocalized bonding patterns. Anionic, neutral, and cationic B₃Si₁₁ clusters have multiplicity of structural forms and their low-lying isomers show dynamical fluxionality. The bond lengths, bond orders, MO, constant electronic charge density surfaces, and PDOS analyses showed that the three B atoms in B₃Si₁₁ have strong bonding interactions.

Structural evolution and electronic properties of CoSin− (n = 3–12) clusters: mass-selected anion photoelectron spectroscopy and quantum chemistry calculations

Experimental measurements and theoretical calculations show that CoSi₁₀⁻ has the highest vertical detachment energy among all the CoSi_n⁻ (n = 3–12) clusters, implying CoSi₁₀⁻ has special stability.

Structural determination of niobium-doped silicon clusters by far-infrared spectroscopy and theory

The structures of niobium doped silicon cluster cations are determined by a combination of infrared multiple photon dissociation spectroscopy and density functional theory calculations.

Investigation on the neutral and anionic BxAlyH2 (x + y = 7, 8, 9) clusters using density functional theory combined with photoelectron spectroscopy

The photoelectron experimental spectra measured at 266 nm and simulated spectra of B₂Al₅H₂⁻ and B₂Al₆H₂⁻ clusters.

Geometry controls the stability of FeSi14

FeSi₁₄ is stable due to its compact and symmetric cage structure highlighting the importance of geometric effects in FeSi_n clusters.

Discovery of a silicon-based ferrimagnetic wheel structure in V(x)Si(12)(-) (x = 1-3) clusters: photoelectron spectroscopy and density functional theory investigation

Our studies show that VSi(12)(-) adopts a V-centered hexagonal prism with a singlet spin state. The addition of the second V atom leads to a capped hexagonal antiprism for V(2)Si(12)(-) in a doublet spin state. Most interestingly, V(3)Si(12)(-) exhibits a ferrimagnetic, bicapped hexagonal antiprism wheel-like structure with a total spin of 4 μ(B).

Does the 18-Electron Rule Apply to CrSi12?

Understanding the bonding between silicon and transition metals is valuable for devising strategies for incorporating magnetic species into silicon. CrSi12 is the standard example of a cluster whose apparent high stability has been explained by the 18-electron rule. We critically examine the bonding and nature of stability of CrSi12 and show that its electronic structure does not conform to the 18-electron rule. Through theoretical studies, we find that CrSi12 has 16 effective valence electrons assigned to the Cr atom and an unoccupied 3dz(2) orbital. We demonstrate that the cluster's apparent stability is rooted in a crystal field-like splitting of the 3d orbitals analogous to that of square planar complexes. CrSi14 is shown to follow the 18-electron rule and exhibits all conventional markers characteristic of a magic cluster.

Structural and magnetic properties of CoGe(n)- (n=2-11) clusters: photoelectron spectroscopy and density functional calculations

A series of cobalt-doped germanium clusters, CoGe(n)(-/0) (n=2-11), are investigated by using anion photoelectron spectroscopy combined with density functional theory calculations. For both anionic and neutral CoGe(n) (n=2-11) clusters, the critical size of the transition from exo- to endohedral structures is n=9. Natural population analysis shows that there is electron transfer from the Ge(n) framework to the Co atom at n=7-11 for both anionic and neutral CoGe(n) clusters. The magnetic moments of the anionic and neutral CoGe(n) clusters decrease to the lowest values at n=10 and 11. The transfer of electrons from the Gen framework to the Co atom and the minimization of the magnetic moments are related to the evolution of CoGe(n) structures from exo- to endohedral.

Study on structures and electronic properties of neutral and anionic TiSin(0,-1)(n = 1–8) clusters using G4 theory

The geometries, electronic structures and energies of small TiSi n species (n = 1–8) and their anions were systematically investigated by G4 theory. The ground-state structures of these clusters are presented herein. For neutral TiSi n (n = 1–8), the spin multiplicities of the ground-state structures are singlet, with the exception of n = 2, which exists in a triplet state. For anionic TiSi n-, the spin multiplicities of the ground-state structures are doublet, with the exception of n = 2, which is quartet. The adiabatic electron affinities for TiSi n are estimated to be 1.31 eV ( TiSi ), 1.46 eV ( TiSi 2), 1.53 eV ( TiSi 3), 1.71 eV ( TiSi 4), 2.06 eV ( TiSi 5), 2.16 eV ( TiSi 6), 2.20 eV ( TiSi 7) and 2.39 eV ( TiSi 8). In comparison with the available experimental data, the calculated adiabatic electron affinities differ from experimental values by an average absolute deviation of only 0.03 eV. Additionally, the dissociation energies of Ti atoms from TiSi n, and Si atoms from TiSi n and Si n clusters are estimated to examine relative stabilities.

Structural evolution and stabilities of negatively charged lead telluride clusters

The equilibrium geometric structures, relative stabilities and electronic properties of negatively charged lead telluride clusters are systematically investigated using density functional theory (DFT). The result offered both vertical and adiabatic detachment energies (VDEs and ADEs) for these clusters, divulging an outline of alternating values in which odd n clusters exhibited higher values than even n clusters. Simulations found the negatively charged lead telluride clusters with even n to be thermodynamically more stable than their immediate odd n neighbors, with a consistent pattern also being found in their HOMO–LUMO (HL) gaps. Analysis of the clusters dissociation energies found at [Formula: see text] cluster to be the preferred product of the queried fragmentation processes, consistent with our finding that [Formula: see text] cluster exhibits enhanced stability. Beyond n = 12, this study showed that the negatively charged ( PbTe )nclusters in the size range n = 13 – 20, prefer two-dimensional stacking of face-sharing lead telluride cubical units, where lead and tellurium atoms possess a maximum of five-fold coordination. The preference for six-fold coordination, which is observed in the bulk, was not observed at these cluster sizes.

Geometries, stabilities and electronic properties of beryllium-silicon Be₂Si(n) clusters

The equilibrium geometries, growth patterns, stabilities, and electronic properties of bimetallic Be₂Si(n) (n = 1-11) clusters are systematically investigated at the B3LYP/6-311G(d) level of theory. Harmonic vibrational analysis has been performed to assure that the optimized geometries are stable. The optimized results suggest that the three-dimensional structures are observed for the most stable isomers of Be₂Si(n) clusters when n > 2. The calculated vertical ionization potential for the lowest-energy isomers are comparable to the experimental values of Si(n+2). According to the averaged binding energy, fragmentation energy, second-order energy difference and HOMO-LUMO gaps calculations, we identify that the Be₂Si₂ and Be₂Si₅ clusters are more stable, and Be atoms doping enhance the chemical reactivity of the Si n host. The natural population and natural electron configuration analyses indicate that the Be atoms possess positive charge at n = 1-5 but negative charge at n = 6-11. The chemical hardness of Be₂Si(n) clusters show three local maxima at n = 2, 5, and 9, whereas three local minima are found for the corresponding chemical potential, meaning these clusters are more stable than their neighboring cluster sizes.

Identification of hyperhalogens in Agn(BO2)m (n = 1–3, m = 1–2) clusters: anion photoelectron spectroscopy and density functional calculations

We identified hyperhalogens in Ag_n(BO₂)_m (n = 1–3, m = 1–2) clusters by using anion photoelectron spectroscopy and density functional calculations.