Structural stability and evolution of terbium-doped silicon clusters and influence of 4f → 5d electronic transition mechanism on magnetism and appearance of photoelectron spectroscopy for TbSin0/− (n = 6-18) clusters

The global minimal structures of terbium-doped Si clusters and their anions TbSi _n^0/− (n = 6-18) are confirmed by employing the ABCluster unbiased global search technique combined with a B2PLYP double-hybrid density functional and comparing consistency of simulated and experimental photoelectron spectroscopy (PES). The results demonstrated that structural evolution patterns for neutral clusters prefer Tb-substitutional to Tb-encapsulated configuration starting from n = 16. While for the corresponding anionic clusters, the growth pattern adopts Tb-linked structures to encapsulated motif. The Natural Population Analysis revealed that the 4f electrons of Tb atom in TbSi _n^0/− (n = 6-18) clusters participate in bonding. The way to participate in bonding is one 4f electron transition to 5d orbital ([Xe]6s²4f⁹ → [Xe]6s²4f⁸5d¹), which significantly affects the cluster's magnetism and appearance of PES. The total magnetic moments of neutral TbSi _n and the corresponding anions maintain at 7 μB and 6 μB, respectively, which are larger than that of an isolated Tb atom. The HOMO-LUMO energy gap, relative stability, and chemical bonding analysis demonstrated that superatomic TbSi₁₆⁻ cluster is a magic cluster with fine thermodynamic and moderate chemical stability.     

Perfect Core-Shell Octahedral B@B38+, Be@B38, and Zn@B38 with an Octa-Coordinate Center as Superatoms Following the Octet Rule

Planar, tubular, cage-like, and bilayer boron clusters B_n^+/0/− (n=3∼48) have been observed in joint experimental and theoretical investigations in the past two decades. Based on extensive global searches augmented with first-principles theory calculations, we predict herein the smallest perfect core-shell octahedral borospherene O_h B@B₃₈⁺ ( 1 ) and its endohedral metallo-borospherene analogs O_h Be@B₃₈ ( 2 ), and O_h Zn@B₃₈ ( 3 ) which, with an octa-coordinate B, Be or Zn atom located exactly at the center, turn out to be the well-defined global minima of the systems highly stable both thermodynamically and dynamically. B@B₃₈⁺ ( 1 ) represents the first boron-containing molecule reported to date which contains an octa-coordinate B center covalently coordinated by eight face-capping boron atoms at the corners of a perfect cube in the first coordination sphere. Detailed natural bonding orbital (NBO) and adaptive natural density partitioning (AdNDP) bonding analyses indicate that these high-symmetry core-shell complexes X@B₃₈^+/0/− (X=B, Be, Zn) as super-noble gas atoms follow the octet rule in coordination bonding patterns (1S²1P⁶), with one delocalized 9c-2e S-type coordination bond and three delocalized 39c-2e P-type coordination bonds formed between the octa-coordinate X center and its octahedral O_h B₃₈ ligand to effectively stabilize the systems. Their IR, Raman, and UV-Vis spectra are computationally simulated to facilitate their spectroscopic characterizations.     

Searching new structures of beryllium-doped in small-sized magnesium clusters: Be2MgnQ (Q = 0, −1; n = 1–11) clusters DFT study

Using CALYPSO method to search new structures of neutral and anionic beryllium-doped magnesium clusters followed by density functional theory (DFT) calculations, an extensive study of the structures, electronic and spectral properties of Be₂Mg_n^Q (Q = 0, −1; n = 2–11) clusters is performed. Based on the structural optimization, it is found that the Be₂Mg_n^Q (Q = 0, −1) clusters are shown by tetrahedral-based geometries at n = 2–6 and tower-like-based geometries at n = 7–11. The calculations of stability indicate that Be₂Mg₅^Q=0, Be₂Mg₅^Q=−1, and Be₂Mg₈^Q=−1 clusters are “magic” clusters with high stability. The NCP shows that the charges are transferred from Mg atoms to Be atoms. The s- and p-orbitals interactions of Mg and Be atoms are main responsible for their NEC. In particular, chemical bond analysis including molecular orbitals (MOs) and chemical bonding composition for magic clusters to further study their stability. The results confirmed that the high stability of these clusters is due to the interactions between the Be atom and the Mg₅ or Mg₈ host. Finally, theoretical calculations of infrared and Raman spectra of the ground state of Be₂Mg_n^Q (Q = 0, −1; n = 1–11) clusters were performed, which will be absolutely useful for future experiments to identify these clusters.     

Computational studies of stable hexanuclear CulAgmAun (l + m + n = 6; l,m, n > 0) clusters

A DFT study was carried out on the ground state structures of ternary Cu_lAg_mAu_n (l + m + n = 6) clusters, with the aim of investigating changes of thermal and kinetic stabilities as an effect of composition, as well as the composition dependence of the electrostatic potential, of stable planar structures. DFT optimizations were performed using the PBE functional and the SDD basis set. All the optimized structures adopt planar geometries with bent triangular structures. Calculated binding energy values are in the range 1.5–1.9 eV/atom, which shows their thermal stability. The predicted HOMO‐LUMO energy gap values are in the semiconductor region, providing a qualitative indication of a moderate kinetic stability. NBO analyses indicate the existence of two mechanisms promoting planar structural stability, one due to bonding‐antibonding orbital interaction, and the other one due to the well‐known spd hybridization. Wiberg indices were obtained showing interatomic bonding. Electrostatic potential calculations show the existence of nucleophilic attack regions preferentially around silver and copper atoms located at the vertices while electrophilic attack regions are found in the vicinity of gold atoms over the cluster plane. Apparently, charge transfer occurs toward gold from silver and copper atoms when the concentration is favorable in the proximity of gold atoms. In particular, if the small ternary clusters discussed here contain only one gold atom, then a high electron density is observed at the site of this gold atom. © 2016 Wiley Periodicals, Inc.     

Photoelectron Spectroscopy and Density Functional Calculations of TiGen- (n=7-12) Clusters

The growth pattern and electronic properties of TiGe_n^- (n=7-12) clusters were investigated using anion photoelectron spectroscopy and density functional theory calculations. For both anionic and neutral TiGe_n clusters, a half-encapsulated boat-shaped structure appears at n=8, and the boat-shaped structure is gradually covered by the additional Ge atoms to form Ge_n cage at n=9-11. TiGe₁₂^- cluster has a distorted hexagonal prism cage structure. According to the natural population analysis, the electron transfers from the Ge_n framework to the Ti atom for TiGe_n^-/0 clusters at n=8-12, implying that the electron transfer pattern is related to the structural evolution.     

VB2n-(n=8~12)团簇几何结构、电子及热力学特性的理论研究

基于卡里普索结构预测程序和密度泛函理论的第一性原理计算,搜索确定了VB_2n^-（n=8~12）团簇的基态和亚稳态结构。结果发现,V原子的掺杂完全改变了原硼团簇的结构并提高了原体系的稳定性。掺杂体系基态结构分别呈现高对称性的鼓状（VB₁₆^-：C_2v）、管状（VB₁₈^-：C_2v和VB₂₀^-：C_s）及笼状（VB₂₂^-：C₂和VB₂₄^-：D_3h）结构。基于基态结构,研究了体系的电荷转移和极化率,拟合出了光电子能谱、红外和拉曼谱图,分析了流变键和芳香特性。最后,研究了体系的热力学特性,讨论了温度对热力学参数的影响。     

The effect of silicon doping on the geometrical structures,stability, and electronic and spectral properties of magnesium clusters: DFT study of SiMgn (n = 1-12) clusters

Using the density functional theory (DFT) method at the B3LYP /6−311G (D) level, we studied how silicon doping affects the geometrical structure, stability, and electronic and spectral properties of magnesium clusters. The stable isomers of SiMg _n (n = 1-12) clusters were calculated by searching numerous initial configurations using the CALYPSO program. The geometrical structure optimization shows that most stable SiMg _n (n = 3-12) clusters are three-dimensional. In addition, geometrical structure growth patterns show that some structures of SiMg _n clusters can be directly formed by replacing one Mg atom in the corresponding Mg _{n + 1} cluster with one silicon atom, such as SiMg₈ and Mg₉ clusters. The stability of SiMg _n clusters is analyzed by calculating the average binding energy, fragmentation energy, and second-order energy difference. The results show that SiMg _n clusters with n = 5 and 8 are more stable than others. MO contents analysis show that the Si 3p-orbitals and Mg 3s-orbital are mainly responsible for the stability of these two clusters. The results of the natural charge population (NCP) and natural electronic configure (NEC) analysis of the electronic properties reveal that the charges in SiMg_n (n = 1-12) clusters transfer from magnesium atoms to silicon frame, and electronic charge distributions are primarily governed by s- and p-orbital interactions. In addition, the Vertical ionization potential (VIP), vertical electron affinity (VEA), and chemical hardness of ground sates of SiMg _n (n = 1-12) clusters were studied in detail and compared with the experimental results. The conclusions show that the chemical hardness of most SiMg _n clusters are lower than that of pure Mg _{n + 1} (n = 1-12) clusters, except for n = 1 and 8. This indicates that the doping of silicon atom can always reduce the chemical hardness of pure magnesium clusters. Finally, the infrared and Raman spectral properties of SiMg₅ and SiMg₈ clusters were calculated and discussed in detail.     

Computer simulation of the structure of large molecules: IV. 2D polybuckminsterfullerenes and their boraza analogs with bisingle nitrogen-boron bonds

The equilibrium structure of the dimer (C₆₀)₂, clusters (C₆₀)₉, and (C₆₀)₇ simulating the poly-C₆₀ (VIII) and poly-C₆₀ (XII), as well as their boraza analogs with bisingle nitrogen-boron bonds was determined by the quantum-chemical methods B3LYP/6-31G and PBE0/6-31G. The boraza analogs are characterized by the positive values of calculated (B3LYP/PBE0) energies of the interpolyhedral bonds: 10/20, 35/74, and 54/109 kcal mol⁻¹ respectively per a pair of monomers. The PBE0 method predicts shorter bond than B3LYP, and, in accordance with calorimetric data, positive bonding energy of the polyhedra in (C₆₀)n.     

Site Preference in Multimetallic Nanoclusters: Incorporation of Alkali Metal Ions or Copper Atoms into the Alkynyl‐Protected Body‐Centered Cubic Cluster [Au7Ag8(C≡CtBu)12]+

The synthesis, structure, substitution chemistry, and optical properties of the gold‐centered cubic monocationic cluster [Au@Ag₈@Au₆(C≡C^tBu)₁₂]⁺ are reported. The metal framework of this cluster can be described as a fragment of a body‐centered cubic (bcc) lattice with the silver and gold atoms occupying the vertices and the body center of the cube, respectively. The incorporation of alkali metal atoms gave rise to [M_nAg_8?nAu₇(C≡C^tBu)₁₂]⁺ clusters (n=1 for M=Na, K, Rb, Cs and n=2 for M=K, Rb), with the alkali metal ion(s) presumably occupying the vertex site(s), whereas the incorporation of copper atoms produced [Cu_nAg₈Au_7?n(C≡C^tBu)₁₂]⁺ clusters (n=1–6), with the Cu atom(s) presumably occupying the capping site(s). The parent cluster exhibited strong emission in the near‐IR region (λ_max=818 nm) with a quantum yield of 2 % upon excitation at λ=482 nm. Its photoluminescence was quenched upon substitution with a Na⁺ ion. DFT calculations confirmed the superatom characteristics of the title compound and the sodium‐substituted derivatives.     

Structures and electronic properties of the small rubidium‐doped silicon RbSin (n = 1–12) clusters

The geometries, relative stabilities, and electronic properties of small rubidium‐doped silicon clusters RbSi_n (n = 1–12) have been systematically investigated using the density functional theory at the B3LYP/GENECP level. The optimized structures show that lowest‐energy isomers of RbSi_n are similar with the ground state isomers of pure Si_n clusters and prefer the three‐dimensional for n = 3–12. The relative stabilities of RbSi_n clusters have been analyzed on the averaged binding energy, fragmentation energy, second‐order energy difference, and highest occupied molecular orbital‐lowest unoccupied molecular orbital energy gap. The calculated results indicate that the doping of Rb atom enhances the chemical activity of Si_n frame and the magic number is RbSi₂. The Mulliken population analysis reveals that the charges in the corresponding RbSi_n clusters transfer from the Rb atom to Si atoms. The partial density of states and chemical hardness are also discussed. © 2014 Wiley Periodicals, Inc.     

Analysis of Why Boron Avoids sp2 Hybridization and Classical Structures in the BnHn+2 Series

We performed global minimum searches for the B_nH_n+2 (n=2‐5) series and found that classical structures composed of 2c–2e B? H and B? B bonds become progressively less stable along the series. Relative energies increase from 2.9 kcal mol^?1 in B₂H₄ to 62.3 kcal mol^?1 in B₅H₇. We believe this occurs because boron atoms in the studied molecules are trying to avoid sp² hybridization and trigonal structure at the boron atoms, as in that case one 2p‐AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p‐AOs and avoiding having one 2p‐AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron–hydride clusters as well as for pure boron clusters and boron compounds in general.     

Revisiting the structural and electronic properties of neutral,mono- and di-anionic titanium-doped silicon clusters TiSin0/−/2− (n = 6-16)

The systematic structures search for neutral and Zintl anionic Ti-doped silicon clusters TiSi_n^0/−/2− (n = 6-16) have been carried out using the ABCluster global search technique combined with a double-hybrid density functional method. Based on the predicted energies, adiabatic electron affinities, vertical detachment energies and the consistency between simulated and experimental photoelectron spectroscopy, the true global minimum structures are confirmed. The results show that structural growth pattern of neutral TiSi_n clusters is from linked structures (n = 10-12) to encapsulated configurations (n = 13-16). In contrast, the evolution pattern of Zintl anionic TiSi_n^−/2− clusters begins with the pentagonal bipyramid structure (n = 6). As the Si atoms increase, these Si atoms attach to the surface adjacent to Ti atom, and gradually surround Ti atom. Eventually, the encapsulated structure is formed when n = 12. Moreover, two extra electrons not only perfect the structure of TiSi₁₂ but also improve its chemical and thermodynamic stability.     

Density functional theory study of the adsorption of NO on CunX (n = 2–8; X = Cu,K) clusters

Density functional theory calculations are performed to analyze the structure and stability of Cu and Cu-K clusters with 3 to 9 atoms. The results indicate that the stability of the clusters decreases after doping with a K atom. With the increase of cluster size, the stability of the clusters shows odd-even alternation. Cu₈ and Cu₇K clusters exhibit the highest stability. Next, different adsorption sites are considered to investigate the geometry of Cu_nNO and Cu_n−1KNO clusters. By calculating the adsorption energy and the HOMO-LUMO energy gap, it is determined that both types of reactions are exothermic processes, indicating stable adsorption of NO. Notably, the Cu_nK clusters are more active (stronger adsorption) for NO than the Cu_n clusters. The most chemically active clusters among Cu_nNO and Cu_n−1KNO clusters are Cu₈NO and Cu₇KNO clusters. Finally, electron transfer and Mayer bond order analysis of Cu₈NO and Cu₇KNO clusters reveal that the N O bond order decreases due to electron transfer when Cu/Cu-K clusters adsorb NO. In this process, the N atom is the electron donor and the Cu atom is the electron acceptor. Fundamental insights obtained in this study can be useful in the design of Cu/Cu-K catalysts.     

3，5-二羟基-2，4，6-三硝基苯酚铷的晶体结构和热行为

0IntroductionSom e nitrogen鄄rich alkaline and alkali鄄earth m et鄄als com pounds of polynitro hydroxybenzenes can beused environm entally friendly prim ary explosives[1￣5].2,4,6鄄Trinitro鄄1,3,5鄄trihydroxybenzene(trinitrophloroglu鄄cinol,TNPG)belongs to a polynitro hydroxybenzeneand has been used in chem icalindustry as an ingredi鄄entfor prim ing com position,percussion caps and deto鄄nator form ulations[6].Therefore,in recent years,ithasbeen exploited to prepare a num ber of salts of ba…     

High Pressure Study of NH4Pb2Br5 Type Compounds. I Structural Parameters and Their Evolution under High Pressure

We have investigated the nature of the interactions of ns²‐cations and the possible structure‐determining role of the ns²electron pair at ambient and high pressure in several AB₂X₅ (A = K, Rb, Cs, In, Tl; B = Sn, Pb, Sr; X = Cl, Br, I) compounds. Structural parameters are obtained by high pressure x‐ray diffraction as well as by quantum mechanical methods (DFT‐GGA‐calculations). The structural parameters at ambient and high pressure are discussed and compared to those of Tl₅Se₂I crystallising in the antitype structure. Short cation—cation distances in the NH₄Pb₂Br₅ type structure enable direct cation—cation interactions and the existence of an ns²‐cation in the B‐position is crucial for the stability of these structures. The effect of pressure on the structural parameters of these compounds gives new insights into the interactions of lone pair cations. The pronounced decrease of the cation—cation distances with pressure points to strongly increasing bonding interactions between the lone pair cations.     

One-Electron Pseudo-Potential Determination of Stable Isomers of the Li*Ar n Excited Clusters: Absorption Spectra

We present pseudo-potential calculations of geometrical structures of stable isomers of LiAr _n clusters with both an electronic ground state and excited states of the lithium atom. The Li atom is perturbed by argon atoms in LiAr _n clusters. Its electronic structure obtained as the eigenfunctions of a single-electron operator describing the electron in the field of a Li⁺Ar _n core, the Li⁺ and Ar atoms are replaced by pseudo-potentials. These pseudo-potentials include core-polarization operators to account for the polarization and correlation of the inert core with the valence Lithium electron [J Chem Phys 116, 1839 1]. The geometry optimization of the ground and excited states of LiAr _n (n = 1–12) clusters is carried out via the Basin-Hopping method of Wales et al. [J Phys Chem 101, 5111 2; J Chem Phys 285, 1368 3]. The geometries of the ground and ionic states of LiAr _n clusters were used to determine the energy of the high excited states of the neutral LiAr _n clusters. The variation of the excited state energies of LiAr _n clusters as a function of the number of argon atoms shows an approximate Rydberg character, corresponding to the picture of an excited electron surrounding an ionic cluster core, is already reached for the 3s state. The result of optical transitions calculations shows that the absorption spectral features are sensitive to isomer structure. It is clearly the case for transitions close to the 2p levels of Li which are distorted by the cluster environment.     

Structural and Electronic Properties of ConC3-/0 and ConC4-/0 (n=1-4) Clusters: Mass-Selected Anion Photoelectron Spectroscopy and Density Functional Theory Calculations

We investigated the structural evolution and electronic properties of Co_nC₃^-/0 and Co_nC₄^-/0 (n=1-4) clusters by using mass-selected photoelectron spectroscopy and density functional theory calculations. The adiabatic and vertical detachment energies of Co_1-4C₃^- and Co_1-4C₄^- were obtained from their photoelectron spectra. By comparing the theoretical results with the experimental data, the global minimum structures were determined. The results indicate that the carbon atoms of Co_nC₃^-/0 and Co_nC₄^-/0 (n=1-4) are separated from each other gradually with increasing number of cobalt atoms but a C₂ unit still remains at n=4. It is interesting that the Co₂C₃^- and Co₂C₄^- anions have planar structures whereas the neutral Co₂C₃ and Co₂C₄ have linear structures with the Co atoms at two ends. The Co₃C₃^- anion has a planar structure with a Co₂C₂ four-membered ring and a Co₃C four-membered ring sharing a Co-Co bond, while the neutral Co₃C₃ is a three-dimensional structure with a C₂ unit and a C atom connecting to two faces of the Co₃ triangle.     

Density functional study of structural and electronic properties of maximum‐spin n+1Aun−1Ag clusters

The structures and relative stabilities of high‐spin ⁿ⁺¹Au_n?1Ag and ⁿAu_n?1Ag⁺ (n = 2–8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high‐spin neutral or cationic Au_n?1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high‐spin neutral or cationic Au_n clusters. The properties of mixed gold–silver clusters are strongly sized and structural dependence. The high‐spin bimetallic clusters tend to be holding three‐dimensional geometry rather than planar form represented in their low‐spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high‐spin clusters, which is different from its position occupied by light atom in the low‐spin situations. Our theoretical calculations indicated that in various high‐spin Au_n?1Ag neutral and cationic species, ⁵Au₃Ag, ³AuAg and ⁵Au₄Ag⁺ hold high stability, which can be explained by valence bond theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Stability,Infrared Spectra and Electronic Structures of (ZrO2)n(n=3-6)Clusters:DFT Study

The stability, infrared spectra and electronic structures of (ZrO₂)_n (n=3–6) clusters have been investigated by using density‐functional theory (DFT) at B3LYP/6‐31G* level. The lowest‐energy structures have been recognized by considering a number of structural isomers for each cluster size. It is found that the lowest‐energy (ZrO₂)₅ cluster is the most stable among the (ZrO₂)_n (n=3–6) clusters. The vibration spectra of Zr? O stretching motion from terminal oxygen atom locate between 900 and 1000 cm^?1, and the vibrational band of Zr? O? Zr? O four member ring is obtained at 600–700 cm^?1, which are in good agreement with the experimental results. Mulliken populations and NBO charges of (ZrO₂)_n clusters indicate that the charge transfers occur between 4d orbital of Zr atoms and 2p orbital of O atoms. HOMO‐LUMO gaps illustrate that chemical stabilities of the lowest‐energy (ZrO₂)_n (n=3–6) clusters display an even‐odd alternating pattern with increasing cluster size.