Density functional theory study of small vanadium oxide clusters

Density functional theory is employed to study structure and stability of small neutral vanadium oxide clusters in the gas phase. BPW91/LANL2DZ level of theory is used to obtain structures of VOy (y=1-5), V2Oy (y=2-7), V3Oy (y=4-9), and V4Oy (y=7-12) clusters. Enthalpies of growth and fragmentation reactions of the lowest energy isomers of vanadium oxide molecules are also obtained to study the stability of neutral vanadium oxide species under oxygen saturated gas-phase conditions. Our results suggest that cyclic and cage-like structures are preferred for the lowest energy isomers of neutral vanadium oxide clusters, and oxygen-oxygen bonds are present for oxygen-rich clusters. Clusters with an odd number of vanadium atoms tend to have low spin ground states, while clusters with even number of vanadium atoms have a variety of spin multiplicities for their ground electronic state. VO2, V2O5, V3O7, and V4O10 are predicted to be the most stable neutral clusters under the oxygen saturated conditions. These results are in agreement with and complement previous gas-phase experimental studies of neutral vanadium oxide clusters.     

Structure and energetics of small gold nanoclusters and their positive ions

We performed density functional theory calculations at the PW91PW91/LANL2DZ, PW91PW91/Stuttgart 1997, PW91PW91/CRENBL, B3LYP/LANL2DZ, and SVWN5/LANL2DZ levels of theory to attain the minimum-energy structures of neutral and cationic gold clusters of up to nine gold atoms. We locate the 2D-to-3D (two-dimensional to three-dimensional) transition in cationic clusters as occurring between Au(8) (+) and Au(9) (+). We also demonstrate that we can correlate the 2D-to-3D transition in cationic clusters with a linear extrapolation of the energy differences of the lowest-lying 2D and 3D structures of cluster sizes below the transition. We then use the same approach to predict that the 2D-to-3D transition occurs in neutral clusters at Au(11); this is confirmed by locating 3D Au(11) structures that are lower in energy than the best 2D structures reported to date. We examine the effects of choice of basis sets and exchange-correlation functionals on the relative stabilities and other properties of the calculated structures. Finally we find that there is good agreement between calculated and experimental data for clusters with up to six constituent atoms. For clusters with more than seven atoms, there are significant differences observed between the calculated and experimental properties using SVWN5/LANL2DZ, but there is still good agreement for the other levels of theory used.     

铁磁性双核吲哚铜配合物的理论研究

采用密度泛函理论结合对称性破损态方法(DFT-BS),以双亚甲胺席夫碱为配体的双核吲哚铜配合物[Cu2L(AZ)(DMSO)](L=双甲亚胺三阴离子,由1-苯基-3-甲基-4-甲酰吡唑和1,3-二氨-2-丙醇衍生而成;AZ=7-氮杂吲哚阴离子)作为研究对象,通过与实验数据相比较,讨论了在不同密度泛函方法与基组对金属铜配物交换耦合常数的影响.结果表明,4种混合密度泛函方法(B3PW91,B3LYP,B3P86和PBE)及3种单一密度泛函(BPW91,BLYP和BP86)的计算结果都与实验值106cm-1有着相同的符号,但使用单一密度泛函所得到的结果与实验值比较接近.不论是混合密度泛函还是单一密度泛函计算所得到的耦合常数Jab对基组都有很大的依赖性,且BLYP/LANL2DZ水平下计算所得结果与实验数据吻合程度最好.研究表明,铁磁性配合物[Cu2L(AZ)(DMSO)]中存在着自旋离域和自旋极化效应.     

Comparison of DFT methods for molecular structure and vibration spectra of ofloxacin calculations

Comparison of the performance of different density functional theory (DFT) methods at various basis sets in predicting molecular and vibration spectra of ofloxacin was reported. The methods employed in this study comprise six functionals, namely, mPW1PW91, HCTH, LSDA, PBEPBE, B3PW91 and B3LYP. Different basis sets including LANL2DZ, SDD, LANL2MB, 6-31g, 6-311g and 3-21g were also examined. Comparison between the calculated and experimental data indicates that the mPW1PW91/6-311g level afford the best quality to predict the structure of ofloxacin. The results also indicate that B3LYP/LANL2DZ level show better performance in the vibration spectra prediction of ofloxacin than other DFT methods.     

Green's function formalism coupled with Gaussian broadening of discrete states for quantum transport: application to atomic and molecular wires

A Green's function formalism incorporating broadened density of states (DOS) is proposed for the calculation of electrical conductance. In cluster-molecule-cluster systems, broadened DOS of the clusters are defined as continuous DOS of electrodes and used to calculate Green's function of electrodes. This approach combined with density functional theory is applied to the electrical transmission of gold atomic wires and molecular wires consisting of benzene-1,4-dithiolate, benzene-1,4-dimethanethiolate, 4,4(')-bipyridine, hexane dithiolate, and octane dithiolate. The B3LYP, B3PW91, MPW1PW91, SVWN, and BPW91 functionals with the LANL2DZ, CEP, and SDD basis sets are employed in the calculation of conductance. The width parameter was successfully determined to reproduce the quantum unit of conductance 2e(2)/h in gold atomic wires. The combination of the B3LYP hybrid functional and the CEP-31G basis set is excellent in reproducing measured conductances of molecular wires by Tao et al. [Science 301, 1221 (2003); J. Am. Chem. Soc. 125, 16164 (2003); Nano Lett. 4, 267 (2004)].     

Modeling the Adsorption of CO on Small Pt,Fe and Co Clusters for the Fischer–Tropsch Synthesis

The adsorption of CO on Fe, Pt and Co clusters was modeled by the DFT approach using the B3LYP and the BPW91 functionals together with the LANL2DZ and the 6-31G(d) basis set. These calculations show that although CO adsorbs more strongly on Pt than on either Fe or Co, the dissociation energy on Fe and on Co is lower than the corresponding dissociation energy on Pt. Therefore, the activation energy for dissociation is not determined by the adsorption energy. Additionaly, the CO bond distances also do not show any correlation to the adsorption energy.     

Hydrogenation reactions of ethylene on neutral vanadium sulfide clusters: experimental and theoretical studies

The reactions of C(2)H(4) with H(2) on neutral vanadium sulfide clusters in a fast flow reactor are investigated by time-of-flight mass spectrometry employing 118 nm (10.5 eV) single photon ionization. The experimental products of these reactions are V(m)S(n)C(2)H(x) (m=1, n=1-3; m=2, n=1-5, and x=4-6). Observation of these products indicates that these V(m)S(n) clusters have high catalytic activity for hydrogenation reactions of C(2)H(4). Density functional theory calculations at the BPW91/TZVP level are carried out to explore the geometric and electronic structures of the V(m)S(n) clusters and to determine reaction intermediates and transition states, as well as reaction mechanisms. All reactions are estimated as overall barrierless or with only a small barrier (0.1 eV), and are thermodynamically favorable processes at room temperature. The ethylene molecule is predicted to connect with active V atoms through its π-orbital or form a σ-bond with active V atoms of catalytic V(m)S(n) clusters. The S atoms bonding with active V atoms play an important role in the dissociation of the H(2) molecule; H atoms transfer to the C(2)H(4) (one after another) following breaking of the H-H bond. A catalytic cycle for C(2)H(4) hydrogenation reactions on a vanadium sulfide catalyst surface is suggested based on our experimental and theoretical investigations.     

Reactions of sulfur dioxide with neutral vanadium oxide clusters in the gas phase. II. Experimental study employing single-photon ionization

Single-photon ionization through vacuum ultraviolet (VUV, 10.5 eV) and soft X-ray (extreme ultraviolet, EUV, 26.5 eV) laser radiation is successfully employed for the study of the reactions of neutral vanadium oxide clusters (V(m)O(n)) with sulfur dioxide (SO2) in the gas phase. V(m)O(n) clusters are generated by reaction of a laser-generated vanadium plasma with O2 in a supersonic expansion. The clusters are cooled in the expansion and are reacted with SO2 in a fast-flow reactor. Detection of neutral clusters and products is through ionization employing VUV and EUV laser radiation and time-of-flight mass spectrometry. Many association reaction intermediates [V(m)O(n)SO2 and V2O4(SO2)2] are observed. Isolated SO is also observed, as a product as predicted by theoretical studies presented in part I (J. Phys. Chem. A 2007, 111, 13339). A weak feature at the SO3 mass channel (80 amu) is suggested to be present in the product mass spectra. Further reactions of the intermediates with O2 are positively identified for VO2SO2, V3O7SO2, and V5O10SO2. Reaction mechanisms are interpreted on the basis of the observations and preliminary theoretical calculations. Molecular level reaction mechanisms for oxidation of SO2 to SO3 facilitated by condensed-phase vanadium oxides as catalysts are suggested.     

Study of Hg22+ and complexes of NpO2+ and UO22+ in solution. examples of cation-cation interactions

Density functional theory (BPW91/TZ2P) is used to explore the nature of cation-cation interactions (CCIs) that exist between two actinyl cations in solution. Solvation, which is modeled using COSMO, favors the complexes (ONpO-ONpO)2+ and (ONpO-OUO)3+ over separated NpO2+(aq) and UO2(2+)(aq) cations because of the quadratic dependence of solvation on charge. For (OUO-OUO)4+, solvation effects, even though very large, are unable to overcome intrinsic electrostatic repulsion between the units. The actinyl-actinyl complexes are T-shaped, with the oxygen of one unit coordinated to the actinide metal of the other unit. The association free energies of (ONpO-ONpO)2+ and (ONpO-OUO)3+ are calculated as -42.1 and -29.2 kcal/mol. Explicit consideration of the first solvation shell at the B3LYP/LANL2DZ level suggests that the free energies of binding may be overestimated. The Hg2(2+) dication, though not considered a "traditional" CCI, is very similar to the actinyl-actinyl interaction. The binding free energy of Hg2(2+) in solution is calculated as -16.0 kcal/mol.     

双环金属铱(Ⅲ)异腈配合物的二阶非线性光学性质

采用密度泛函理论(DFT)方法对双环金属Ir(III)异腈配合物的非线性光学(NLO)性质进行计算研究。用B3PW91(UB3PW91)(金属原子采用LANL2DZ基组,非金属原子采用6-31G*基组)方法对配合物进行几何结构优化。在优化构型基础上,采用B3PW91(UB3PW91)和B3LYP(UB3LYP)方法计算了配合物的第一超极化率(βtot),并用CAM-B3LYP(UCAM-B3LYP)(金属原子采用LANL2DZ基组,非金属原子采用6-31G**基组)方法模拟配合物的吸收光谱。结果表明,主配体的取代基(R1)和副配体的取代基(R2)对第一超极化率值贡献不大。配合物发生氧化还原反应,电荷转移方式增多,电荷转移程度增大,使βtot值显著增加,其中1a+([(C∧N)2Ir(CNR)2]+(R=CH3))发生氧化反应和还原反应的βtot值分别增大了75倍和144倍。因此,这类双环金属铱(III)异腈配合物的氧化还原反应可以有效地调节其二阶NLO性质。     

Small Ligated Organometallic $${{\hbox {Pd}}}_{n}$$ Clusters ($$n= 4{-}12$$n=4-12): A DFT Investigation

DFT calculations were carried out at the BP86/LANL2DZ level of theory to probe the structures and relative stabilities of small and medium size ligated palladium clusters. Results show that optimized geometries satisfactorily mimic experimental structural data. Observed cluster electron counts generally deviate from the expected Wade–Mingos electron counts because of the presence of several non-conical T-shaped \({\hbox {ML}}_{3}\) fragments in the clusters. These species are thermodynamically stable with substantial HOMO–LUMO gaps.     

Theoretical insight into structural and electronic properties of cationic Scn+ (n=2-13): A benchmark study

Geometric, thermodynamic and electronic properties of cationic scandium clusters are studied. Geometric optimizations and stable spin states of Sc₂⁺ are assessed on high level ab-initio coupled cluster method CCSD(T) with different dunning correlation consistent basis sets (aug-cc-pVDZ, aug-cc-pVTZ and aug-cc-pVQZ). Then, 23 DFT functionals belonging to different classes are evaluated at 6-31G (d), LANL2MB, LANL2DZ and Def2-SVP basis sets, and the results are compared with the benchmarked coupled cluster calculations. Due to excellent correlation, PBEPBE/LANL2DZ was chosen to perform calculation of higher scandium cationic clusters Sc_n⁺ (n = 3-13). In addition, we explored relative stability, binding energies, second order energy differences, vertical ionization energies, vertical electron affinities and HOMO-LUMO gaps. Moreover, these results are also compared with the neutral scandium clusters.     

Density functional calculation of the structure and electronic properties of Cu(n)O(n) (n = 1-8) clusters

Ab initio simulations and calculations were used to study the structures and stabilities of copper oxide clusters, Cu(n)O(n) (n = 1-8). The lowest energy structures of neutral and charged copper oxide clusters were determined using primarily the B3LYP/LANL2DZ model chemistry. For n ≥ 4, the clusters are nonplanar. Selected electronic properties including atomization energies, ionization energies, electron affinities, and Bader charges were calculated and examined as a function of n.     

DFT studies on the tetranuclear cubane complex [Ni4(ampd)4(Cl4)]·MeCN

Density functional theory (DFT) is used to investigate the structural properties of Ni(II) cubane [Ni₄(ampdH)₄Cl₄]·MeCN. The structural features and ground state geometry calculations are computed at the B3LYP/6-31G* (LANL2DZ) level of theory. We shed light on the highest occupied molecular orbital and lowest unoccupied molecular orbital. The absorption spectrum is calculated using time-dependent DFT. The absorption wavelengths are calculated using different functionals, i.e., pw91pw91, B3LYP, BHandHLYP, CAM-B3LYP, LC-BLYP, and M06. The LC-BLYP is in good agreement with the experimental data.     

Experimental and theoretical study of the reactions between neutral vanadium oxide clusters and ethane, ethylene, and acetylene

Reactions of neutral vanadium oxide clusters with small hydrocarbons, namely C2H6, C2H4, and C2H2, are investigated by experiment and density functional theory (DFT) calculations. Single photon ionization through extreme ultraviolet (EUV, 46.9 nm, 26.5 eV) and vacuum ultraviolet (VUV, 118 nm, 10.5 eV) lasers is used to detect neutral cluster distributions and reaction products. The most stable vanadium oxide clusters VO2, V2O5, V3O7, V4O10, etc. tend to associate with C2H4 generating products V(m)O(n)C2H4. Oxygen-rich clusters VO3(V2O5)(n=0,1,2...), (e.g., VO3, V3O8, and V5O13) react with C2H4 molecules to cause a cleavage of the C=C bond of C2H4 to produce (V2O5)(n)VO2CH2 clusters. For the reactions of vanadium oxide clusters (V(m)O(n)) with C2H2 molecules, V(m)O(n)C2H2 are assigned as the major products of the association reactions. Additionally, a dehydration reaction for VO3 + C2H2 to produce VO2C2 is also identified. C2H6 molecules are quite stable toward reaction with neutral vanadium oxide clusters. Density functional theory calculations are employed to investigate association reactions for V2O5 + C2H(x). The observed relative reactivity of C2 hydrocarbons toward neutral vanadium oxide clusters is well interpreted by using the DFT calculated binding energies. DFT calculations of the pathways for VO3+C2H4 and VO3+C2H2 reaction systems indicate that the reactions VO3+C2H4 --> VO2CH2 + H2CO and VO3+C2H2 --> VO2C2 + H2O are thermodynamically favorable and overall barrierless at room temperature, in good agreement with the experimental observations.     

Theoretical and Experimental Studies on the Metal Complex of Diethylenetriamino-trioxo-molybdenum(Ⅵ)[MoO3(NH2C2H4NHC2H4NH2)]

For diethylenetriamino-trioxo-molybdenum(VI), density functional theory (DFT) method calculations of the structure, atomic charge distributions, electronic spectra, natural po- pulation analyses and thermodynamic properties at different temperatures have been performed by B3LYP method using LANL2DZ, CEP-121G and CEP-31G basis sets, respectively. The calculated results show that B3LYP/LANL2DZ method can best reproduce the molecular structure. The atomic charge distribution analyses indicate that during forming the complex, the ligand of diethyl- enetriamine donates negative charges to MoO3 and these charges are accepted by molybdenum(VI) atom as well as three oxygen atoms. The electronic spectra calculations indicate that B3LYP/ LANL2DZ results are nearest to experimental data among the three methods and electronic tran- sitions are mainly derived from the contribution of bands π→π*. The calculation of the second order optical nonlinearity was carried out, and the molecular hyperpolarizability was 0.7881*10-30 esu.     

Theoretical and Experimental Studies on the Metal Complex of Diethylenetriamino-trioxo-molybdenum(VI) [MoO_3(NH_2C_2H_4NHC_2H_4NH_2)]

1 INTRODUCTION Molybdenum is a biologically important trace ele- ment that occurs in the redox-active sites of moly- bdoenzymes involving in nitrogen, sulfur or carbon metabolism. The structural chemistry of molybde- num complexes has aroused considerable interest in view of its higher oxidation states to form a number of compounds containing MoO groups, and informa- tion on these is very useful in understanding the behavior of MO groups generally[1~3]. Molybdenum oxide-based solids hav…     

A DFT study on Cu(I) coordination in Cu‐ZSM‐5: Effects of the functional choice and tuning of the ONIOM approach

The coordination of Cu⁺ at the T1 and T7 positions of the M7 ring of Cu‐ZSM‐5, and the interaction of NO with coordinated Cu⁺ were investigated by means of DFT/ONIOM calculations. The B3LYP, BLYP, PBE1PBE, PBE, M06, and M062X functionals with the def2‐TZVP (def2‐QZVP for Cu) basis set were used in the high‐level part of ONIOM calculations, with the HF/3‐21G, B3LYP/LANL2DZ, M06/LANL2DZ, and M062X/LANL2DZ methods in the low‐level part. The ability of suitable combinations of the above methods to reproduce (i) the crystallographic structure of purely siliceous ZSM‐5, (ii) the tendency of Cu⁺ to be twofold or fourfold coordinated by framework oxygen atoms of Cu‐ZSM‐5, and (iii) the interaction energy and the N? O stretching frequency of adsorbed nitrogen oxide are discussed, showing that different results are obtained depending on the adopted computational approach. With reference to above properties, some considerations about the employment of the ONIOM approximations are also included. © 2015 Wiley Periodicals, Inc.     

杂硼原子簇XB6+ (X=C,Si, Ge,Sn, Pb)的稳定性和芳香性

利用从头算MP2方法和密度泛函理论B3LYP和B3PW91方法, 研究了杂硼原子簇XB₆⁺ (X=C, Si, Ge, Sn, Pb)的结构、稳定性及化学键合情况. 对C, Si, Ge, B使用6-311+G(d)基组, 对Sn和Pb使用LANL2DZ赝势基组. 研究结果表明, 具有C_s对称性的假平面XB₆⁺ (X=C, Si, Ge, Sn, Pb)结构是势能面上的全域极小点, 其稳定性要高于C_6v对称性的锥形结构和C₂对称性的假锥形结构. 在B3LYP水平上, 对这些异构体的势能面的极小点进行了自然键轨道(NBO)的分析; 对最稳定构型的最高占据分子轨道(HOMO)和最低空轨道(LUMO)能级差、分子轨道(MO)和核独立化学位移(NICS)进行了计算和讨论. 分析了杂原子和硼原子间、相邻硼原子间的键合情况, 讨论了最稳定构型的芳香性质.