Theoretical Investigation of LaC~n and La_2C~n(n=-1,0,+1)Clusters

用密度泛函方法研究了ＬａＣｎ及Ｌａ２Ｃｎ（ｎ＝－１，０，＋１）分子簇的结构和稳定性．对Ｌａ２Ｃｎ体系，提出了两种可能构型，其中一种具有Ｃ２ｖ对称性，另一种具有Ｄ∞ｈ对称性．计算结果表明，对Ｌａ２Ｃｎ，当ｎ＝＋１，－１时，线状结构最稳定，并且在ｎ＝＋１时，Ｃ２ｖ结构极不稳定有收敛向线状结构的趋势．而当ｎ＝０时，Ｃ２ｖ结构最稳定．最后还计算了ＬａＣ和Ｌａ２Ｃ分子簇的电子亲和势和离化能．     

Theoretical Investigations on the Structures and Properties of the Side-on Complexes B_2(N_2)_2 and Monocyclic B_n(N_2)_n~m (n=3～6,m=-1～+2)

The structures and energies of the side-on complexes B2(N2)2 and monocyclic Bn(N2)nm (n = 3～6,m = -1～+2) between N2 (1∑+g) and B (2P) have been investigated by the DFT-B3LYP and MP2 methods at the 6-311+G(2d) and aug-cc-pVTZ levels. The analyses of NICS (Nucleus Independent Chemical Shifts),NBO (nature bond orbital),AIM (atoms in molecules) and frontal orbitals have been used to reveal the origin of coordination bond between the π-electron donor N2 group and B atom,accompanied by the comparison with the end-on complexes. The results have indicated that the side-on coordination complexes can be formed due to the relative strong fluidity of the π-electrons,and the nature of the coordination bond has been exposed to be that the N2 group offers 1πu electron to the 2p orbital of boron. The coordinate energies of the side-on complexes are less than those of the end-on complexes. Furthermore,the aromaticity of side-on coordination complex is weaker than that of the corresponding end-on coordination complex.     

ADF Studies of Neutral Small C_n(n=3～6)High-symmetry Clusters

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First-principle Study of AunSc (n=2～13) Clusters

The geometries, stabilities, electronic, and magnetic properties of Au_nSc clusters have been systematically investigated by density functional theory. The lowest energy structures of Au_nSc favor planar structure and the doped Sc atom does not disturb the frame of Au_nclusters with n≤11. For n≥12, Sc atom is fully encapsulated by the Au cages. From theanalysis of the second-order energy difference, the fragmentation energies, vertical ionizationpotential, vertical electron affinity, and HOMO-LUMO gap, the clusters with odd Au atoms possess relatively higher stabilities than their neighbor size. The doping of Sc atom can greatly improve the stability and change the sequence of chemical activity for Au_n. For n≤11, the total magnetic moments of Au_nSc appear the alternation between 0.00 and 1.00 μB. The total magnetic moments are quenched when Sc is trapped into the Au cages with n≥12.     

Theoretical Studies of the Electronic Structures and Spectrum Properties of Pt n Ni m (n + m = 7, n, m ≠ 0) Clusters

We studied Pt _n Ni _m (n + m = 7, n, m ≠ 0) clusters within the framework of the density functional theory (B3LYP) at the LANL2DZ level. The calculated results show that the Fermi levels are determined by the number of Pt atoms, which gain electrons from Ni atoms. Meanwhile, multifarious orbital hybridization is found in the frontier molecular orbital, and the more platinum or nickel atoms, the smaller energy gap it has. Moreover, the calculated IR and Raman spectrum indicates the aromatic character, which is vital for transitional metal clusters.     

Atomistic Structures,Stabilities, Electronic Properties,and Chemical Bonding of Boron–Aluminum Mixed Clusters B3Al n 0/−/+ (n = 2–6)

Journal of Cluster Science - Neutral, anionic, and cationic B3Al n 0/?/+ (n?=?2–6) clusters were systematically explored using density functional theory and coupled cluster...     

Probing the Structures and Properties of Asymmetric Clusters (CH3ClBN3)n (n = 1–6) with Density Functional Theory

Russian Journal of Physical Chemistry A - The structures, stabilities, IR spectrum and thermodynamic properties of small asymmetric clusters (CH3ClBN3)n (n = 1–6) are probed using density...     

Theoretical Studies on the Structures and Stabilities of Charged, Titanium-Doped, Small Silicon Clusters, TiSi n ? /TiSi n + (n?=?1–8)

The structures and stabilities of charged, titanium-doped, small silicon clusters TiSi _n ⁺ /TiSi _n ^? (n?=?1–8) have been systematically investigated using the density functional theory method at the B3LYP/6-311+G* level. For comparison, the geometries of neutral TiSi_n clusters were also optimized at the same level, although most of them have been reported previously (Guo et al., J Chem Phys 126: 234704, 2007). Our results indicate that all neutral TiSi_n clusters favor Si-capped TiSi_n?1 structures, with the lowest energy structure of TiSi₂, TiSi₃, TiSi₄, TiSi₅, TiSi₆, TiSi₇ and TiSi₈ being Si-side-on TiSi adduct, Si-face-capped TiSi₂ triangle, Si-face-capped TiSi₃ trigonal pyramid, Si-face-capped TiSi₄ trigonal bipyramid, Si-face-capped TiSi₅ square bipyramid, Si-face-capped TiSi₆ pentagonal bipyramid, and Si-face-capped TiSi₇ capped pentagonal bipyramid, respectively. The ground state structures obtained herein for the neutral TiSi_n clusters agree well with those of Guo et al. except for TiSi₃ and TiSi₈. Adding or removing an electron greatly changes some ground state structures, i.e. for TiSi₃ ^?/TiSi₃ ⁺, TiSi₅ ^?, TiSi₆ ^?/TiSi₆ ⁺ TiSi₇ ^? and TiSi₈ ^?/TiSi₈ ⁺; others are almost unchanged, e.g. TiSi₂ ^?/TiSi₂ ⁺, TiSi₄ ^?/TiSi₄ ⁺, TiSi₅ ⁺ and TiSi₇ ⁺. Based on the optimized geometries, various energetic properties, including binding energies, fragmentation energies, second-order difference energies, HOMO–LUMO energy gaps, ionization potentials and electron affinities, were calculated for all the most stable isomers. The average binding energies reveal that all of TiSi_n/TiSi _n ⁺ /TiSi _n ^? (n?=?1–8) clusters can continue to gain energy as the size increasing. The fragmentation energies and second-order energy differences suggest that neutral TiSi₅, anionic TiSi₅ ^? and cationic TiSi₆ ⁺ are relatively stable.     

Comparison of Si_n~+ and Ge_n~+(n=2―15) Cationic Structures

We designed and optimized a large number of the isomers of Si12+ at the level of density functional theory (DFT)-B3LYP/6-311++G(d) using the Gaussian 03 software package. An unambiguous structure of the Si12+ cluster is presented, whose IR spectrum agrees well with the experiment result. The most stable geometric structures of Gen+(n=2―15) clusters were determined by the all-electron PBE/DND method in DMol3 of the Material Studio Package, and compared with those of the corresponding Sin+ geometries. Most st...     

Ceometries,Energetics and Spectroscopic Properties of Oxygen Clusters Oxy (x=2～6, y=-2～2)

The geometries, energetics and spectroscopic properties of oxygen clusters, Oxy(x=2~6, y=-2~2), were investigated at the B3LYP/6-311G (d, p) level. The CASSCF calculations were carried out for the ground and excited states of3O2and2O2+. The total energy is3O2(3Σg-)<2O2-(2Πgi)<1O2(1Δg)<1O2-2(1Σg+)<2O2+(2Πg)<1O2+2(1Σg+). The relative energy of the active doublet anion of oxygen molecule,2O2-(2Πgi), is only 28 kJ/mol higher than the triplet neutral oxygen molecule,3O2(3Σg-). The calculated O-O vibrational frequencies all are in good agreement with the experimental values. They are 1577 (1580), 1139 (1090), 1563 (1484), 627 (615~545) and 1993 (1905) cm-1, where the O-O vibrational frequency values in parentheses are experimental values, for3O2(3Σg-),2O2-(2Πgi),1O2(1Δg),1O2-2(1Σg+) and2O2+(2Πg), respectively. Moreover, the O-O vibrational frequency of1O2+2(1Σg+) was computed as 2368 cm-1which has not been reported before at both experimental and theoretical levels. Both bent and linear geometries of O3were studied. The bent-types of O3are more favorable than the linear-type in energy. Three types of structure for oxygen trimers are calculated at the B3LYP/6-311G (d, p) level. They are the structure-I with an obtuse angle of O-O-O,the structure-II with an acute angle of O-O-O, and the structure-III of linear type. For a bent-type structure of O3species (structure-I), the total enegy is2O3-(2B1)<1O3(1A1)<3O3(3B2)<1O3-2(1A1)<2O3+(2A1). The optimization of geometry at B3LYP/6-311G (d, p) level indicated that the species of2O3-(2B1) with 1.3573 of O-O bond length and 115.6584o of O-O-O bond anger is the ground state of O3. The total energy of O4species and their ions is2O4-(Cs,2A′, bend-type)<2O4-(C2v,2A2,face-centered triangle-type)<2O4-(D∞h,2Σg, linear-type)<1O4(Cs,1A′, bend-type)<1O4(D∞h,1Σg, linear-type)<1O4(D4h,1A1g, square-type)<1O4(C2v,1A1, face-centered triangle-type)<2O4-(D4h,1A1g, square-type)<2O4+(D∞h,2Σg, linear-type)<2O4+(Cs,1A′, bend-type). The species with the lowest relative energy is an anion,2O4-(Cs,2A′, bendtype), with chair form geometry and characteristic vibronic frequencies of 1179 and 1349 cm-1. The relative energy of1O5(C2v,1A1) with coplanar-triangle-bicone geometry is the lowest among the O5species and their ions, which may be a resonance structure with1O5(C2v,1A1) of A type. Their characteristic vibronic frequency is 1302 cm-1. The relative energy of the O6species and their ions with hexagon geometry is lower than one with linear geometry. Their infrared vi-bronic intensity may be weak and unobservable but the Raman vibronic intensity may be strong and observable based on their symmetry.     

Stable Structure and Characteristic Spectroscopy of(CH3COCH3)n(n=1～7)Clusters

The stable acetone molecule clusters have been studied by using Beeke's threeparameter(B3LYP)density functional theory(DFT)with standard 6-31G(d)basis set.The calculated results show that the optimal structures of acetone clustets are cyclic and the cycles become larger and larger with the increase of cluster size.The strongest vibration peaks for neutral clusters are C=O stretching vibration.The C=O stretching peaks of cyclic acetone clusters split into double ones when n≥3,the frequencies are red-shifted and corresponding intensities increase with the increase of cluster size.     

DFT Studies on the Stoichiometric Thorium Oxide Clusters(ThO_2)_n(n = 1～5): Electronic and Structural Properties

Density functional theory(DFT) calculations are performed to investigate the electronic and structural properties of the stoichiometric thorium oxide clusters(ThO_2)_n-/0(n = 1～5). Generalized Koopmans' theorem is applied to predict the vertical detachment energies(VDEs)which are used to simulate the anionic photoelectron spectra(PES). Molecular orbital analyses are performed as well to analyze the chemical bonding in these thorium oxide clusters. The results show that the ground states of(ThO_2)_n-/0(n = 1～5) clusters prefer the low-spin structures. With increasing of the cluster size(n), the structure parameters of(ThO_2)_n-/0(n = 1～5) gradually evolve toward bulk thorium oxide species. It shows that both the coordination number and the average bond length increase gradually in(ThO_2)_n-/0(n = 1～5) to approach that of ThO2 bulk. What's more, the vibration frequencies of Th=O double bonds are found to be decreasing along with the increased cluster size.     

Theoretical Study on the Electronic Structures of Small TinNm （n ＋ m = 5, 6） Clusters

45 isomers of TinNm （n ＋ m = 5, 6） clusters, including linear, some planar and some stero configurations, have been predicted by density functional theory method. For five-atom clusters Ti3N2 and Ti2N3, the most stable structures are trigonal bipyramid in D3h symmetry, and for TiaN cluster, the isomer with one nitrogen atom occupying the center of quasi-tetrahedron is the most stable. In the isomers of Ti4N2 and Ti3N3, the planar networks are more stable, but for Ti2N4, the six-membered ring configuration is the most favorable. Most linear structures can form weak-strong bonds alternately with higher energy. As regards to planar structures, the more Ti-N bonds are formed, the more stable they will be; for stero closed polyhedral isomers, their energies are lower.     

Study of Structures and Electronic Properties of Pdn-1Pb and Pdn(n≤8) Clusters

Geometric and electronic properties of Pdn-1Pb and Pdn(n≤8) clusters have been studied by using density functional theory with effective core potentials, focusing on the differences between mono- and bimetallic clusters. The average bond length of Pdn-1Pb (n≤8) bimetallic clusters is longer than that of pure palladium clusters except for n = 2 and 3. The most stable structure of Pdn-1Pb (n≤7) is the singlet where there is at least a Pd or Pb atom on its excited state. The energy gaps of Pd-Pb binary clusters are narrower than those of Pdn clusters, and then the chemical activity is strengthened when Pdn clusters are doped with Pb.     

Onset of Amorphous Structure in CaCO3: Geometric and Electronic Structures of (CaCO3) n (n?=?2–7) Clusters by Ab Initio Calculations

Electronic structures, vibrational analyses, stabilization energies and amorphicity were analyzed for the most stable configurations of the neutral gas phase clusters of calcium carbonate (CaCO₃) _n (n?=?2?C7). Minimum-energy structures were generated through simulated annealing using a mix of molecular dynamics/semiempirical optimization and then full optimization at the ab initio level (RHF/6-31G*). HF-level results are calibrated versus MP2/6-31G* results. Though many clusters are symmetric, the structural arrangements are not crystalline and resemble neither calcite nor aragonite. In general, greater symmetry means a lower stabilization energy. The BSSE- and zero point energy-corrected stabilization energies appear to plateau at about ?113?kcal/mol when n?=?7. Amorphous clusters start appearing when n?=?4 and the lowest-energy minima for n????5 are of C₁ symmetry. No solvent effect is necessary to induce amorphism.     

Structural,Electronic and Magnetic Properties of Co_nO(n = 2～10) Clusters: A Density Functional Study

The structural, electronic, and magnetic properties of Co_nO(n = 2～10) clusters have been systematically investigated within the framework of the generalized gradient approximation density functional theory. The results indicate that the O atom occupies the surface-capped position on Co_nO(n = 2～10) clusters. The stabilities of the host clusters are improved by adding one O atom. Maximum peaks of the second-order difference energy of the ground-state Co_nO clusters are found at n = 3, 6 and 8, indicating higher stability than their neighboring clusters. Compared with corresponding pure Con clusters, the O-doped cobalt clusters have larger gaps between the HOMO and LUMO energy levels, indicating their higher chemical stabilities. In addition, the doping of O atom exhibits different influence on the magnetism of the clusters. This is also further investigated by the local magnetic moment, deformation charge density and partial local density of states analysis.     

Structures and Vibrational Spectra of C_2 and LaC_2~ Clusters

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