Clusters of hydrated methane sulfonic acid CH3SO3H.(H2O)n (n = 1-5): a theoretical study

Ab initio and density functional methods have been used to examine the structures and energetics of the hydrated clusters of methane sulfonic acid (MSA), CH3SO3H.(H2O)n (n = 1-5). For small clusters with one or two water molecules, the most stable clusters have strong cyclic hydrogen bonds between the proton of OH group in MSA and the water molecules. With three or more water molecules, the proton transfer from MSA to water becomes possible, forming ion-pair structures between CH3SO3- and H3O+ moieties. For MSA.(H2O)3, the energy difference between the most stable ion pair and neutral structures are less than 1 kJ/mol, thus coexistence of neutral and ion-pair isomers are expected. For larger clusters with four and five water molecules, the ion-pair isomers are more stable (>10 kJ/mol) than the neutral ones; thus, proton transfer takes place. The ion-pair clusters can have direct hydrogen bond between CH3SO3- and H3O+ or indirect one through water molecule. For MSA.(H2O)5, the energy difference between ion pairs with direct and indirect hydrogen bonds are less than 1 kJ/mol; namely, the charge separation and acid ionization is energetically possible. The calculated IR spectra of stable isomers of MSA.(H2O)n clusters clearly demonstrate the significant red shift of OH stretching of MSA and hydrogen-bonded OH stretching of water molecules as the size of cluster increases.     

小分子硫原子团簇的结构稳定性

用分子图形软件设计出68种硫原子团簇S_3～S_(13)的结构,使用B3LYP密度泛函进行几何构型优化和振动频率计算,排除了振动频率为负值的非局域极小点的结构,根据分子的总能量得出最稳定的同分异构体。在硫原子团簇中,除了部分原子采用一、三配位之外,大部分原子为二配位成键,带三配位的硫原子团簇的总能量较高,硫原子团簇难以生成高配位的笼状结构。从S_5开始链状结构能量高于环状,中性大分子硫原子团簇多呈链状结构。     

硫原子团簇负离子的螺旋结构

在使用B3LYP密度泛函进行几何构型优化和振动频率计算得到的硫原子团簇负离子的结构中,分子的总能量最低的S9- 到 S13-的同分异构体呈螺旋状构型。另外也计算了螺旋状的Sn- (n = 14~20)的结构。大多数的的硫负离子是链状结构,这与相应中性硫原子团簇的环状构型完全不同。     

A density functional study for the isomers of anionic sulfur clusters Sn− (n=3–20)

The signals of anionic sulfur clusters are intense in the mass spectrum of sulfur clusters generated in direct laser vaporization. We have acquired numerous isomers of sulfur clusters by means of the B3LYP DFT method. According to total energies, the most stable S_n⁻ (n=3–13) isomers are predicted. The helical S_n (n=14–20) structures are also calculated. Most of the anionic clusters are with chain configurations; the ring clusters with threefold atom(s) are higher in total energy. The most stable forms of isomers, from S₉⁻ to S₁₃⁻, show helical configurations that are completely different from those of the corresponding neutral and cationic clusters.     

Multiscale approach to explore the potential energy surface of water clusters (H2O)nn <or= 8

We propose a multiscale method to explore the energy landscape of water clusters. An asynchronous genetic algorithm is employed to explore the potential energy surface (PES) of OSS2 and TTM2.1-F models. Local minimum structures are collected on the fly, and the ultrafast shape recognition algorithm was used to remove duplicate structures. These structures are then refined at the B3LYP/6-31+G* level. The number of distinct local minima we found (21, 76, 369, 1443, and 3563 isomers for n = 4-8, respectively) reflects the complexity of the PES of water clusters.     

Chemical Bonding of Transition‐Metal Co13 Clusters with Graphene

We carried out density functional calculations to study the adsorption of Co₁₃ clusters on graphene. Several free isomers were deposited at different positions with respect to the hexagonal lattice nodes, allowing us to study even the hcp 2d isomer, which was recently obtained as the most stable one. Surprisingly, the Co₁₃ clusters attached to graphene prefer icosahedron‐like structures in which the low‐lying isomer is much distorted; in such structures, they are linked with more bonds than those reported in previous works. For any isomer, the most stable position binds to graphene by the Co atoms that can lose electrons. We find that the charge transfer between graphene and the clusters is small enough to conclude that the Co–graphene binding is not ionic‐like but chemical. Besides, the same order of stability among the different isomers on doped graphene is kept. These findings could also be of interest for magnetic clusters on graphenic nanostructures such as ribbons and nanotubes.     

Structures and relative stability of medium-sized silicon clusters. V. Low-lying endohedral fullerenelike clusters Si31-Si40 and Si45

We have performed unconstrained search for low-lying structures of medium-sized silicon clusters Si(31)-Si(40) and Si(45), by means of the minimum-hopping global optimization method coupled with a density-functional based tight-binding model of silicon. Subsequent geometric optimization by using density-functional theory with the PBE, BLYP, and B3LYP functionals was carried out to determine the relative stability of various candidate low-lying silicon clusters obtained from the unconstrained search. The low-lying characteristics of these clusters can be affirmed by comparing the binding energies per atom of these clusters with previously determined lowest-energy clusters(Si(n)) in the size range of 21相似文献   

Theoretical infrared spectrum of the ethanol hexamer

The hydrogen bond network of ethanol clusters is among the most complex hydrogen bond networks of molecular clusters. One of the reasons of its complexity arises from the number of possible ethanol monomers (there are three isoenergetic isomers of the ethanol monomer). This leads to difficulties in the exploration of potential energy surfaces (PESs) of ethanol clusters. In this work, we have explored the PES of the ethanol hexamer at the MP2/aug-cc-pVDZ level of theory. We have provided structures and their relative stability at 0 K and for temperatures ranging from 20 to 400 K in the gas phase. These structures are used to compute the theoretical infrared (IR) spectrum of the ethanol hexamer at the MP2/aug-cc-pVDZ level of theory. As a result, 98 different structures have been investigated, and six isomers are reported to be the most isoenergetically stable structures of the ethanol hexamer. These isomers are folded cyclic structures in which the stability is enhanced by the implication of CH⋯O interactions. Our investigations show that the PES of the ethanol hexamer is very flat, yielding several isoenergetic structures. Furthermore, we have noted that several isomers contribute to the population of the ethanol hexamer at high temperatures. As far as the IR spectroscopic study is concerned, we have found that the IR spectra of the most stable structures are in good agreement with the experiment. Considering this agreement, these structures are used to assign the experimental peaks in the CH-stretching region. We concluded that the stability of the structures of the ethanol hexamer is related both to OH⋯O hydrogen bonds and CH⋯O interactions. Overall, we have found that the IR spectrum of the ethanol hexamer, calculated from the contribution of all the possible stable structures weighted by their probability, excellently reproduce the experimental spectrum of the ethanol hexamer.     

Electronic structure and stability of AlnPn (n = 2-4) clusters

The geometry, electronic configurations, harmonic vibrational frequencies, and stability of the structural isomers of aluminum phosphide clusters have been investigated using the density functional theory. For dimers and trimers, the lowest energy structures are cyclic (IIs, IIIs) with D(nh) symmetry. The caged structure with Td symmetry (Xs) lie lowest in energy among the tetramers. The Al--P bond dominates the structures for many isomers so that one preferred dissociation channel is loss of the AlP monomer. The hybridization and chemical bonding in the different structures are also discussed. Comparisons with silicon and boron nitride clusters, the ground state structures of Al(n)P(n) clusters are analogous to those of their corresponding Si(2n) counterparts. This similarity follows the isoelectronic principle.     

Hydrogen Bond Cooperativity and the Three‐Dimensional Structures of Water Nonamers and Decamers

Broadband rotational spectroscopy of water clusters produced in a pulsed molecular jet expansion has been used to determine the oxygen atom geometry in three isomers of the nonamer and two isomers of the decamer. The isomers for each cluster size have the same nominal geometry but differ in the arrangement of their hydrogen bond networks. The nearest neighbor O? O distances show a characteristic pattern for each hydrogen bond network isomer that is caused by three‐body effects that produce cooperative hydrogen bonding. The observed structures are the lowest energy cluster geometries identified by quantum chemistry and the experimental and theoretical O? O distances are in good agreement. The cooperativity effects revealed by the hydrogen bond O? O distance variations are shown to be consistent with a simple model for hydrogen bonding in water that takes into account the cooperative and anticooperative bonding effects of nearby water molecules.     

Structures and dynamics of protonated ammonia clusters

The structures and infrared spectra of protonated ammonia clusters NH(4+)(NH3)n, for n < or = 8, are investigated using density functional-theory (DFT) calculations and semiempirical DFT/molecular dynamics simulations. For n < 5 the clusters are found to be mostly stable up to 100 K, while the larger clusters (n > or = 5) isomerize. Temperature effects are taken into account by performing ab initio molecular dynamics simulations with the computationally tractable self-consistent charges density functional tight-binding method. The infrared spectra at 10 K for the most stable isomers for n = 3-8 compare qualitatively with predissociation experiments, and using a common scaling factor almost quantitative agreement is found. For n > or = 6 the notion of multiple isomers present under the experimental conditions is supported. Of the 13 stable structures for n = 8 only three are found to survive at 100 K. All other clusters isomerize. Cluster structures are inferred from the analysis of the cumulative radial distribution function of the ammonia molecules surrounding the NH(4+) core. The infrared spectra are found to be typical for the structure of the clusters, which should help to relate the experimentally measured infrared spectra to the number and identity of the contributing isomers. For clusters that reorganize to a more stable isomer during the dynamics, the infrared spectrum is generally similar to that of the stable isomer itself. The clusters are found to preferably form globular structures, although chain-like arrangements are also among the low-energy configurations.     

Low-lying isomers of Si(n)(+) and Si(n)(-) (n=31-50) clusters

We carry out a systematic search for the atomic structures of silicon cluster cations and anions in the size range n=31-50 using density functional theory in the generalized-gradient approximation. The obtained lowest-energy candidates feature cagelike structures. We find that the computed binding energies and the dissociation pathways as well as the mobilities of our lowest-energy isomers of the cations are all in good agreement with the measured data from experiments. Furthermore, based on these isomers, we reveal that the steplike feature appearing in the measured high-resolution mobilities can be correlated with the corresponding fullerenes explicitly, which strongly support the notion that endohedral silicon fullerenelike structures are the most favored growth pattern for silicon clusters in the range n=31-50. Our calculation and analysis suggest that the proposed isomers are probably very close to the major-abundance isomers observed in experiments.     

The conversion among various B4C clusters: a density functional theoretical study

Geometry optimizations and vibration frequencies of B4C clusters were performed with Becke-3LYP method using 6-31G(d) basis set. We have found 14 stable isomers, and the most stable structure among them is the five-member ring containing two three-member boron rings. We also analyzed these stable isomers in detail, and the results show that the structures containing three-member boron rings are predominant in energy for B4C clusters. In terms of MO and NBO analysis, the three-centered bond and the pi-electron delocalization play an important role in stabilizing the planar five-member rings of these B4C clusters. Our calculations suggest that isomer4 can be converted into isomer7 with only an energy barrier of 0.31 kJ mol(-1) at the B3LYP/6-311G+(3df) level. Although the planar structures of the five-member rings (isomers12-14) can be converted with each other, the conversions of isomer14 to isomer13 and isomer13 to isomer12 have high-energy barriers of 70.99 and 68.51 kJ mol(-1) at the B3LYP/6-31G(d) level, respectively.     

Isomer selective infrared spectroscopy of neutral metal clusters

We report experimental infrared spectra of neutral metal clusters in the gas phase. Multiple photon dissociation of the argon complexes of niobium clusters is used to obtain vibrational spectra in the 80-400 cm(-1) region. The observed spectra for Nb(9)Ar(n) (n=1-4) are different for different values of n. This is explained by the presence of two isomers of Nb(9) that have different affinities towards Ar and the isomer specific infrared spectra are obtained. The structures of the isomers are determined by comparing the observed spectra with the outcome of density-functional theory calculations.     

Crystal structures and electronic properties of BaC_2 isomers by theoretical study based on DFT

Band structures and electronic properties of two BaC2 isomers were calculated by using density func-tional theory(DFT) properly.The ionic bond features are all typical between cation(Ba) and anion clusters(C2) in both structures of the isomers.However,a much stronger covalent bond exists in anion clusters which can be seen by inspecting the electron distribution contour that has a dull bell like shape between two carbon atoms.The shortest distance between Ba2 and C22? and the bond length in anion clusters are different in these isomers of BaC2,which are 0.2945 nm and 0.1185 nm for the structure with the I4/mmm space group and 0.2744 and 0.1136 nm with the C2/c type,respectively.Band structures were clarified by combining the DOS to indicate the ionic bonding features more clearly.Population analysis provided further evidence on these ideas.Thermodynamical calculation results reveal that the transition temperature of these two polymorphs of BaC2 locates near 132 K,which is consistent with the recent experimental results.     

Experimental and theoretical studies of the conformational structures of the mixed clusters of 1-cyanonaphthalene with water

A concerted experimental (mass-selective, double-resonance laser spectroscopic technique) and theoretical (correlated quantum chemistry calculation) study of hydrogen-bonded clusters of 1-cyanonaphthalene (CNN) with water has been carried out to probe geometrical structures of the conformational isomers. The structures of the two low-energy conformers of CNN-H2O and CNN-(H2O)2, calculated at the MP2/cc-pVDZ level of theory, are consistent with the mass-selective infrared-ultraviolet double-resonance spectra and the partially resolved rotational band contours of the S1 <-- S0 origin bands. The facile loss of a neutral water molecule from the cluster ion of CNN-(H2O)2, relative to that of CNN-H2O, is in accord with the proposed structures of the clusters.     

小分子硫原子团簇正离子的结构稳定性

用分子图形软件设计出49种硫原子团簇Sn+(n=3～13)的结构,使用B3LYP密度泛函进行几何构型优化和振动频率计算,根据分子的总能量得出最稳定的同分异构体.在硫原子团簇正离子中,大部分原子为二配位成键.带有一、三配位的原子结构的总能量较高.部分最稳定硫原子团簇正离子的构型与最稳定的中性硫原子团簇的构型完全不同.     

氮笼N12的量子化学研究

采用量子化学从头算方法研究了7个氮笼N₁₂,其中包括以前文献中研究过的两个氮笼N₁₂.在RHF/6-31G^*理论水平下进行全构型优化、振动频率分析和热化学计算.计算结果表明,7个结构均是势能面上的局域极小点.N₁₂(D_3d)是所有7个笼状异构体中最稳定的.能量分析表明,如果这些分子能够被合成,将会成为潜在的高能量密度材料.     

Structures of manganese polysulfides: mass-selected photodissociation and density functional calculations

Manganese polysulfide cations, MnS(x)(+) (x = 1-10), were studied with mass-selected photodissociation experiments and density functional calculations. We found that MnS(+), MnS(2)(+) and MnS(3)(+) undergo dissociation at 355 nm by loss of S, S(2) and S(3), respectively. The dissociation of larger clusters is relatively complex because of the existence of multiple isomers and multiple dissociation channels. The geometric structures of the low-lying isomers found by theoretical calculations are consistent with the dissociation channels observed in the experiments. The dissociation of MnS(x)(+) clusters occurs mainly by breaking of the Mn-S bonds since they are weaker than the S-S bonds.