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The analysis presents a theoretical study on the assembly and stabilization of the magic cluster, [Al.sub.4][N.sup.-] into molecular systems in sandwich-like forms. The results show that this cluster can also be used as a new superatom due to its high structural and electronic integrity.

A systematic density functional theory (DFT) calculations is performed on the stabilities and electronic properties of two different structures [Csub.58][X.sub.18] and [C.sub.58][X.sub.1], where X = H, F, and Cl. It is seen that the large energy gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbital and the aromatic character possess high stabilities.

A series of multiply N-confused porphyrins and their Zn and Cu complexes are investigated by using density functional theory (DFT) and ZINDO/SOS methods. The findings demonstrate that the multiply N-confused results have shown that the one-photon absorption (OPA) spectra of multiply N-confused porphyrins, along with their metal complexes and derivatives are promising molecules, which can be assembled series of materials with large two-photon absorption (TPA) cross sections.

A series of ferrocenyl derivatives with TCF-type acceptors are designed, and their electronic structures and one- and two-photon absorption properties are investigated. Results reveal that ferrocenyl derivatives with TCF-type acceptors are promising candidates for two-photon absorptions (TPA) materials.

The characteristics of antiaromatic ring [pi] multi-hydrogen bonds {[H.sub.2]O}[.sub.n] - [C.sub.4][H.sub.4] (n = 1, 2) complexes are studied. One [H.sub.2]O forms a [pi] H-bond with [C.sub.4][H.sub.4] in two ways, one strong pi H-bond part is always accompanied by another H-bond part which is either a weak [pi] H-bond or [pi]-type H-bond.

The stable structures, energies, and electronic properties of neutral, cationic, and anionic clusters of Al(sub n) (n=2-10) are studied and show that the optimized structure of the clusters are more stable than corresponding ones previously reported and the stability has an odd/even alternation phenomenon. Studies on the structures of the Al(sub n)O (n=2-10) clusters show that oxygen is absorbed at the surface or inserted between Al atoms.

The complex singlet potential energy surface for the reaction of CH2OH with NO2 is explored theoretically and the initial association between CH2OH and NO2 is found to be the carbon-to-nitrogen approach forming an adduct with no barrier, followed by C-N bond rupture. A mechanistic comparison is made with the reactions CH3+NO2and CH3O+NO2, to understand the mechanism of the reaction and NO2 combustion chemistry.

The radical-radical reaction between the ketenyl radical (HCCO) and nitrogen dioxide (NO2) played a very important role in atmospheric and combustion chemistry. The result can lead to a deep understanding of the mechanism of the title reaction and can be helpful for understanding NO(sub x) combustion chemistry.

A detailed theoretical study is carried out for the unknown HCO/HOC + C(sub 2)H(sub 2) reactions at the CCSD(T)/6-311G(2d,p)//B3LYP/6-311G(d,p)+ZPVE, Gaussian-3//B3LYP/6-31G(d), and Gaussian-3//MP2(full)/6-31G(d) levels. For the HCO/HOC + C(sub 2)H(sub 2) reaction, both the most feasible C-addition channel and the slightly less competitive H-donation channel lead to P(sub 1) C(sub 2)H(sub 3) +CO.

The computational study of the complex singlet potential energy surface for the reactions of CN with NO(sub 2) including 9 minimum isomers and 10 transition states is illustrated. The study indicates that the title reaction proceeds mostly through singlet pathways and also gives an understanding on the mechanism of the title reaction and is helpful for understanding NO(sub 2)-combustion chemistry.

The multichannel reactions, HOCl + F -> products and HOBr + F -> products are investigated using the dual-level direct dynamics method. Results reveal that for the F + HOCl reaction, the reaction occurs exclusively through the hydrogen abstraction, while both hydrogen and bromine abstractions are involved in the F + HOBr reaction.

A detailed computational study is conducted on the radical-molecule reaction between the vinyl radical (C2H3) and formaldehyde (h2CO). At the Gaussian-3//B2LYP/6-31G(d) and CBS-QB3 levels, the direct H-abstraction forming C2H4+HCO has barriers of 3.9 and 4.7 kcal/mol, respectively.

The structures, energetic, spectroscopies, and isomerization of various doublet Si2CP species are explored theoretically. Implications in interstellar space and P-doped SiC vaporization processes are discussed.

A brief description on a preliminary theoretical study on the SiCN(super +)/SiNC(super +) + H2O reactions is presented. The results provide useful mechanistic information for the analogous ion-molecule reactions of the monovalent silicon-bearing ions.

A detailed potential-energy surface of C4P is established. This involves 12 minimum isomers and 27 interconversion transition states at the Becke exchange functional and nonlocal LYP correlation functional (B3LYP), quadratic configuration interaction method with single and double substitutions (QCISD), and couple cluster method with single, double and noniterative triple substitutions (CCSD(T)) (single-point) levels.

The proton transfer in NH3--HCl by only one molecule of catalyst was studied by using the MP2 method with the large 6-311++G(2d,2p) basis set. The results showed that the proton transfer occurred from HCl to NH3 when catalyst molecule A not only as a proton donor strongly donated the proton to the Cl atom, but as an acceptor strongly accepted the proton from the NH3 molecule in the cyclic H-bond structure.

The study obtained a complete description of the first hyperpolarizabilities of (HCN)n...Li and Li...(HCN)n (n=1,2,3). It indicates that these new alkali metal-molecular clusters have large nonlinear optical responses.

An investigation on the intermolecular interaction effects on the static electric properties by ab initio calculations for four dimers between two pi-systems is presented. It concluded that electron correlation effects are quite important for the calculation of the static electric properties, particularly the first and second hyperpolarizabilities.

A theoretical investigation is conducted on the dynamical properties for the two hydrogen-abstraction reactions of 1,1,1-trichlorethane (CH3CCl3) and 1,1,1-trifluoroethane (CH3CF3) with chlorine atoms over the temperature range 200-1200 K. The theoretical results indicate that for title reactions the vibrational effect is small over the whole considered temperature range and the small-curvative tunneling effect is important in the lower temperature range.

The investigation of the potential energy surface of C2H2FO at CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level. The results show that isomers of 1, 3, 4, 5, 5', 8, 9, and 9' are stable, and the energy barriers are more than 30 kcal/mol.

The hydrogen abstraction reaction OH +HBr right arrow H2O with a small barrier is studied. Results indicate that a variational effect should be considered for the rate constants at high temperatures.

An exploration of the potential energy surfaces of the interstellar molecule SiC2N at the B3LYP/6-311G(d), QCISD/6-311G(D) and CCSD(T)/6-311G(2d) (single point) levels is presented. The calculated bond lengths, harmonic vibrational frequencies, dipole moments, rotational constants and the first excitation energies derived here can assist in future laboratory and interstellar identification of the three SiC2N isomers SiCCN, SiCNC, and SiNCC.

A detailed investigation of the complex potential energy surface for the reaction of singlet methylene (CH2) with Nitrous oxide (N2O) using B3LYP/6-31G(d,p) and single point QCISD(T)/6-311G(d,p) methods is presented. This work can assist experiments to identify the products of the CH2+NO2 reaction.

The complex singlet potential energy surface of the CHNO2 system is investigated to explore the possible reaction mechanism of CH radical with NO2. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are obtained.

Hydrogen abstraction reactions of hydrogen atom with germane and silane were studied by using ab initio molecular orbital theory and canonical vibrational transition state theory. The reaction rate constants in the temperature range 200-2600 k are calculated by the canonical variational transition state theory (CVT) with small curvature tunneling (SCT) correlation.

The three structures of rare gas inserted fluorohydrides HRgF (Rg=He, Ar, and Kr) with all real frequencies are obtained at the QCISD(T)/aug-cc-pVTZ level. The static first hyperpolarizabilities (β0) at the QCISD/aug-cc-pVQZ level are 8 a.u. (HF), 384 a.u. (HHeF), 737 a.u. (HArF), and 465 a.u. (HKrF). The β0 value remarkably increases by about 50–90 times from 8 a.u. (HF) to 384–737 a.u. (HRgF) due to the inserted rare gas (Rg). The Rg atomic number dependence of β0 for HRgF (Rg=He, Ar, and Kr) is found at the first time. The order of β0 is unmonotonic to be HHeFHKrF, but not monotonic (HHeF0 relates to both the geometric effect (expanded H...F distance by Rg) and the electronic effect of Rg. From HHeF to HArF and from HArF to HKrF, the preponderant effect on β0 is variational. From HHeF to HArF, the geometric effect is preponderant and the β0 value increases; from HArF to HKrF, the electronic effect of Rg is preponderant and the β0 value decreases. Thus, the rare gas atomic number dependence of β0 is unmonotonic. Furthermore, as the order of β0 is consistent with that of the difference between the ground and excited-state dipole moments (Δμ), the Δμ may be one mainly controlling factor of β0. The nature of H–Rg bond is also explored that special short H–He bond of 0.811 Å is only a half single bond due to its Wiberg bond index of 0.51, while the long H–Ar and H–Kr bonds are almost single bond with the Wiberg bond index of about 0.8. [ABSTRACT FROM AUTHOR]

The hydrogen abstraction reactions of fluoroalkane isomers CF2HCFHCF2H and CF3CFHCFH2 with the OH radicals have been studied theoretically by a dual-level direct dynamics method. Optimized geometries and frequencies of all the stationary points and extra points along the minimum-energy path are obtained at the BB1K/6-31+G(d,p) level of theory, and then the energy profiles are refined at G3(MP2) level of theory. Using the improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling correction (SCT), the rate constants for each channel are calculated over a wide temperature range of 200–1000 K. Our results show that the tunneling correction plays an important role in the rate constant calculation in the low temperature range. The calculated ICVT/SCT rate constants are consistent with available experimental data. Our calculations indicate the contribution of the abstraction from the –CFH– group of isomeric compounds CF2HCFHCF2H and CF3CFHCFH2 to the overall reactions is quite different over the whole temperature range due to the effect of different groups at both sides of –CFH– group. Furthermore, to further reveal the thermodynamic properties, the enthalpies of formation of the two reactants CF2HCFHCF2H, and CF3CFHCFH2, and the product radicals CF2HCFCF2H, CF2HCFHCF2, CF3CFCFH2, and CF3CFHCFH are obtained by using isodesmic reactions. [ABSTRACT FROM AUTHOR]

The geometrical structure, electronic structure, one-photon absorption (OPA) and two-photon absorption (TPA) properties of the perylene tetracarboxylic derivatives (PTCDs) were studied theoretically by using density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods. The results revealed that increasing the number of naphthalene nucleus, extending the conjugated length on long axis, increasing the strength of donor group on lateral side, decreasing the ΔEH-L (energy gap between the highest occupied orbital and the lowest unoccupied orbital) and keeping the conjugation effect and inductive effect along the same molecular axis are the efficient ways to enlarge TPA cross section of PTCDs compounds. The results that PTCDs compounds exhibited extremely large TPA cross section of around 800–1100 nm (near infrared region) shed light into the significance of the PTCDs compounds for applications in TPA labeling materials in vivo. [ABSTRACT FROM AUTHOR]

All the 924 classical isomers of fullerene C56 have been investigated by PM3, and some most stable isomers are refined with HCTH/3-21G and B3LYP/6-31G(d) methods. D2:003 with the least number of adjacent pentagons is predicted to be the most stable isomer at B3LYP/6-31G(d) level, while Cs:022 and C2:049 possess nearly degenerate energies with relative energies of 0.03 and 3.90 kcal/mol, respectively. However, as to dianionic C562- fullerene, C2v:011 is predicted to be the most stable isomer. Investigations also show that the encapsulation of Ca atom in C56 fullerene is exothermic and the metallofullerenes Ca@C56 can be described as Ca2+@C562-. The computed relative stabilities show that the D2:003 behaves more thermodynamically stable than other isomers in a wide temperature interval, and C2v:011 should also be an important component. The electronic isomerization of C56 (C2v:011) and C50 (D5h:002) indicates that this phenomenon might be rather general in fullerenes and causes different properties, thus bringing about new possible applications of fullerenes. The static second-order hyperpolarizabilities of the three most stable isomers are slightly larger than that of C60. [ABSTRACT FROM AUTHOR]

The 437 classical isomers of fullerene C52 have been studied by PM3, HCTH/3-21G, and B3LYP/6-31G(d). C2:029 with the least number of adjacent pentagons is predicted to be the most stable isomer. The investigations show that both the number of adjacent pentagons and the degree of aromaticity play important roles in the relative stabilities of fullerene isomers. To clarify the relative stabilities of the C52 isomers in a wide range of temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP/6-31G(d) level. C2:029 prevails in a wide temperature range. In addition, the electronic spectra and second-order hyperpolarizabilities are determined by means of ZINDO and sum-over-states model. The static second-order hyperpolarizability of C2:029 is 51% larger than that of C60. Furthermore, intensity-dependent refractive index γ (-ω;ω,ω,-ω) (ω=1.1653 eV) of C2:029 is 13 times larger than that of C60. The encapsulation of Ca atom in C52 fullerene is exothermic and the metallofullerene Ca-C52 is described as Ca2+-C522-. [ABSTRACT FROM AUTHOR]

Polycoordinate planar B compounds BXn (X=B, Al, C, N and Si; n=3–8) are optimized at B3LYP/6-311++G (3df,p) theoretical level. For X=B, center B atom can coordinate three to eight atoms, while for X=Al, C, Si, and N, it can only coordinate three to five atoms. The natural bond orbital analysis shows that the center B atom does not violate the octet rule, though the numbers of coordinated atom even reach 8. According to molecular orbital analysis and nucleus independent chemical shift value calculation, it seems that these polycoordinate planar B compounds BXn (X=B, Al, C, N, and Si; n=3–8) hold twofold (α and π) aromatic, which play an important role in their stability and keeping all atoms in one plane. [ABSTRACT FROM AUTHOR]

A new kind of single-electron lithium bonding complexes H3C...LiY (Y=H, F, OH, CN, NC, and CCH) was predicted and characterized in the present paper. Their geometries (C3v) with all real harmonic vibrational frequencies were obtained at the MP2/aug-cc-pVTZ level. For each H3C...LiY complex, single-electron Li bond is formed between the unpaired electron of CH3 radical and positively charged Li atom of LiY molecule. Due to the formation of the single-electron Li bond, the C–H bonds of the CH3 radical bend opposite to the LiY molecule and the Li–Y bond elongates. Abnormally, the three H3C...LiY (Y=CN, NC, and CCH) complexes exhibit blueshifted Li–Y stretching frequencies along with the elongated Li–Y bonds. Natural bond orbital analyses suggest ca. 0.02 electron transfer from the methyl radical (CH3) to the LiY moiety. In the single occupied molecular orbitals of the H3C...LiY complexes, it is also seen that the electron could of the CH3 radical approaches the Li atom. The single-electron Li bond energies are 5.20–6.94 kcal/mol for the H3C...LiY complexes at the CCSD(T)/aug-cc-pVDZ+BF (bond functions) level with counterpoise procedure. By comparisons with some related systems, it is concluded that the single-electron Li bonds are stronger than single-electron H bonds, and weaker than conventional Li bonds and π-Li bonds. [ABSTRACT FROM AUTHOR]

In the present study, an attempt is made to reveal the main mechanism of photodissociation on the lowest-lying Rydberg state 1B1 of ketene, referred to as the second singlet excited state S2, by means of the complete active space self-consistent field and the second-order multiconfigurational perturbation theory methods. The located S2/S1/T1 three-surface intersection plays an important role in the dissociation process. It is shown that the intersection permits an efficient internal conversion from S2 to S1 state, but prohibits the intersystem crossing from S2 to T1 state because of the small spin-orbital coupling value of 0.136 cm-1. The main photodissociation process could be described as follows: after one photon absorption to the S2 state, ketene preferentially relaxes to the minimum S2_C2v, and undergoes a transition state S2_TS with small potential barrier along the Cs-I (out-of-plane bent) symmetry, and passes through the S2/S1/T1 intersection to reach S1 surface, then arrives at the transition state S1_TS along the minimum energy path. As is well known, S1→S0 internal conversion around the Franck-Condon region is expected to be very efficient, and eventually the hot S0 molecule has accumulated enough energy to yield the CH2 (ã 1A1) and CO (X 1Σ+) products. [ABSTRACT FROM AUTHOR]

The electronic structures and stabilities of cationic MPb12+ clusters (M=B, Al, Ga, In, and Tl) with 50 valence electrons are investigated within density functional theory. It is shown that, at the B3LYP/cc-pVDZ(-PP) and BPW91/cc-pVDZ(-PP) levels of theory, the structures of MPb12+ with icosahedra (Ih) symmetry are energetically favorable, and their high stabilities may arise from the closed-shell nature of the π subsystems which are subject to the 2(Nπ+1)2 rule with Nπ=1. In addition, the possessing of large nucleus-independent chemical shifts of the five kinds of clusters reflects the common aromatic character of these clusters. From the comparison of our studies on the binding energies and the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gaps, the cluster AlPb12+ has higher stability than the others and this is consistent with the recent mass-spectrometric discovery of Al-doped Pbn+ clusters, in which AlPb12+ is highly abundant. The same methods are used to search for the structures of the neutral MPb12 clusters. The calculations reveal that the most stable geometries of the BPb12 and GaPb12 clusters have Ih symmetry, the AlPb12 and InPb12 clusters have Th symmetry, and the TlPb12 cluster has C5v symmetry. Furthermore, the vertical ionization potentials of the neutral MPb12 clusters are smaller than that of some alkali atoms, indicating that the neutral MPb12 clusters possess superalkali character. [ABSTRACT FROM AUTHOR]

Theoretical studies of the solvated electrons (HCN)n- (n=3, 4) reveal a variety of electron trapping possibilities in the (HCN)n (n=3, 4) clusters. Two isomers for (HCN)3- and four isomers for (HCN)4- are obtained at the MP2/aug-cc-pVDZ+dBF (diffusive bond functions) level of theory. In view of vertical electron detachment energies (VDEs) at the CCSD(T) level, the excess electron always “prefers” locating in the center of the system, i.e., the isomer with higher coordination number shows larger VDE value. However, the most stable isomers of the solvated electron state (HCN)3- and (HCN)4- are found to be the linear C∞ν and D∞h structures, respectively, but not the fullyl symmetric structures which have the largest VDE values. [ABSTRACT FROM AUTHOR]

Using the dissipative particle dynamics simulation technique, we have studied the influence of the molecule rigidity on the nanostructures of the A2(B4)2-type miktoarm block copolymers. A typical spherical micellar ordered structure is obtained for a coil-coil miktoarm block copolymer in melt. By introducing a bond angle potential in our model to enhance the molecule rigidity systematically, we find, respectively, a hexagonal cylindrical structure and a parallel ellipsoid in lamellae structure which is discovered for the first time. [ABSTRACT FROM AUTHOR]

The D3d and D2d isomers of the Li3–O–Li3 molecule are metal-nonmetal-metal sandwichlike structures that contain two Li3 superalkali atoms. Their geometries and the real frequencies are obtained at the CCSD(T)/aug-cc-pVDZ level. They are different from the traditional types of the nonmetal-metal-nonmetal sandwich compounds. The natural bond orbital calculation and the topological property ∇2ρ(r) calculation indicate that they are typical ionic compounds. In two isomers, the O2- anion is sandwiched in between two Li3+ cation rings. However, the different orientations of two Li3+ planes give the D3d isomer its own special characteristics. Under the action of the O2- anion in the center, the valence electrons of the D3d isomer are pushed out from two Li3+ triangle rings. This special interaction causes three phenomena. First, the valence electron clouds are distended. Second, the vertical ionization energy of the D3d isomer is considerably low, 4.39 eV, so that it may also be viewed as a superalkali atom. Third, we find that the D3d isomer owns the out-of-plane aromaticity and the largest negative nucleus-independent chemical shift value (-10.8 ppm) exists at 2.5 Å above the center of the Li3+ ring, not at the center of the Li3+ ring like the isolated aromatic Li3+ cation. [ABSTRACT FROM AUTHOR]

By the counterpoise geometry optimization at the level of CCSD(T)/aug-cc-pVDZ, the asymmetrical linear structures with all the real frequencies were obtained for the triatomic cations of (ABA)+ type: Ne3+, (He–Ne–He)+, (Ar–Ne–Ar)+, (Ar–He–Ar)+, (He–O–He)+, and (Ar–O–Ar)+. The validity of this optimization method is confirmed by comparing with the method of the potential-energy surface for the calculations of Ne3+ and (He–Ne–He)+. Using the molecular-orbital theory, it is found that the interaction within the triatomic cations is dominated by the contribution from the first two atoms while the contribution from the third atom is small. This result is justified as a direct consequence of forming an asymmetrical linear structure. Specifically, four types of interaction within the triatomic cations are identified: three-electron σ-type hemibond, three-electron π-type hemibond, two-electron σ bond, and the attraction between cation and atoms. For Ne3+, (He–Ne–He)+, and (He–O–He)+ clusters, it is shown that the electron correlation effect supports the asymmetry. [ABSTRACT FROM AUTHOR]

A detailed theoretical study is performed on the hitherto unknown germanium cyanide radical and its ions. The 2Π state GeCN lies 5.0 kcal/mol lower than the 2Π state GeNC at the coupled-cluster theory including single and double excitations and perturbative inclusion of triple excitations [CCSD(T)]/6-311++G(3df)//quadratic configuration interaction with single and double excitations (QCISD)/6-311G(d)+zero-point vibrational energy (ZPVE) level. For interconversion between them, two electronic state pathways 2A′ and 2A″ are located, with the latter being 0.7 kcal/mol more favorable than the former. On the 2A″ path, the GeCN→GeNC and GeNC→GeCN conversion barriers are 14.5 and 9.5 kcal/mol, respectively. The detailed singlet and triplet potential-energy surfaces of both the cationic and anionic GeCN species are also investigated. On the ground-state electronic hypersurface, singlet GeNC+ is 4.6 kcal/mol more stable than singlet GeCN+, whereas triplet GeNC- is 10.0 kcal/mol less stable than triplet GeCN-. The relative energy difference between the GeCN0,± and GeNC0,± can be well correlated with the number of vacant orbitals on the Ge atom. The stability of the neutral and ionic CGeN and cyclic cGeCN is also discussed. The predicted structures, spectroscopies, ionization, and affinity energies as well as the Renner–Teller properties are expected to provide reliable estimates for future characterization of the potential GeCN and GeNC radicals as well as their ionic counterparts both in the laboratory and in the interstellar space. [ABSTRACT FROM AUTHOR]

The title unknown reaction is theoretically studied at various levels to probe the interaction mechanism between the ethynyl radical (HC=C·) and formaldehyde (H2C==O). The most feasible pathway is a barrier-free direct H-abstraction process leading to acetylene and formyl radical (C2H2+HCO) via a weakly bound complex, and then the product can take secondary dissociation to the final product C2H2+CO+H. The C-addition channel leading to propynal plus H-atom (HCCCHO+H) has the barrier of only 3.6, 2.9, and 2.1 kcal/mol at the CCSD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p)+ZPVE, CCSD(T)/6-311+G(3df,2p)//QCISD/6-311G(d,p)+ZPVE, and G3//MP2 levels, respectively [CCSD(T)—coupled cluster with single, double, and triple excitations; ZPVE—zero-point vibrational energy; QCISD—quadratic configuration interaction with single and double excitations; G3//MP2—Gaussian-3 based on Moller–Plesset geometry]. The O addition also leading to propynal plus H atom needs to overcome a higher barrier of 5.3, 8.7, and 3.0 kcal/mol at the three corresponding levels. The title no-barrier reaction presents a new efficient route to remove the pollutant H2CO, and should be included in the combustion models of hydrocarbons. It may also represent the fastest radical-H2CO reaction among the available theoretical data. Moreover, it could play an important role in the interstellar chemistry where the zero- or minute-barrier reactions are generally favored. Discussions are also made on the possible formation of the intriguing propynal in space via the title reaction on ice surface. [ABSTRACT FROM AUTHOR]

Dissipative particle dynamics, a simulation technique appropriate at mesoscopic scales, has been applied to investigate the interfaces in immiscible binary A/B homopolymer blends and in the ternary systems with their block copolymers. For the binary blends, the interfacial tension increases and the interface thickness decreases with increasing Flory–Huggins interaction parameter χ while the homopolymer chain length is fixed. However, when the χ parameter and one of the homopolymer chain length is fixed, increasing another homopolymer chain length will induce only a small increase on interfacial tension and slight decrease on interface thickness. For the ternary blends, adding the A-b-B block copolymer will reduce the interfacial tension. When the mole number of the block copolymer is fixed, longer block chains have higher efficiency on reducing the interfacial tension than the shorter ones. But for the block copolymers with fixed volume fraction, shorter chains will be more efficient than the longer ones on reducing the interfacial tension. Increasing the block copolymer concentration reduces interfacial tension. This effect is more prominent for shorter block copolymer chains. [ABSTRACT FROM AUTHOR]

Lowe–Andersen (LA) temperature controlling method [C. P. Lowe, Europhys. Lett. 47, 145 (1999)] is applied in a series of mesoscopic polymer simulations to test its validity and efficiency. The method is an alternative for dissipative particle dynamics simulation (DPD) technique which is also Galilean invariant. It shows excellent temperature control and gives correct radial distribution function as that from DPD simulation. The efficiency of LA method is compared with other typical DPD integration schemes and is proved to be moderately efficient. Moreover, we apply this approach to diblock copolymer microphase separation simulations. With LA method, we are able to reproduce all the results from the conventional DPD simulations. The calculated structure factors of the microphases are consistent with the experiments. We also study the microphase evolution dynamics with increasing χN and find that the bath collision frequency Γ does not affect the order of appearing phases. Although the thermostat does not affect the surface tension, the order-disorder transition (ODT) is somewhat sensitive to the values of Γ, i.e., the ODT is nonmonotonic with increasing Γ. The dynamic scaling law is also tested, showing that the relation obeys the Rouse theory with various Γ. [ABSTRACT FROM AUTHOR]

The gas-phase ion-molecule reactions play very important roles in interstellar and in plasma chemistry. Motivated by recent astrophysical detection of the SiCN/SiNC radicals and laboratory characterization of some SiCN-containing species, we carried out a detailed potential energy survey on the SiCN+/SiNC++H2O reaction at the Becke's three-parameter Lee–Yang–Parr-B3LYP/6-311G(d,p) and coupled cluster with single, double, and triple excitations-CCSD(T)/6-311+G(2df,p) (single-point) levels as an attempt towards understanding the SiCN+/SiNC+ reaction mechanisms. In contrast to the carbene-featured analogous CCN+/CNC++H2X (X=O,S) reactions, the title reaction SiCN+/SiNC++H2O are not associated with any competitive silylene-insertion characters. Moreover, the –CN↔–NC interconversion has a low barrier and plays an important role in determining the final product distributions. This is also in marked difference from the CCN+/CNC+ reaction. It is shown that the isomeric sila-cations SiCN+ and SiNC+ can both react with H2O to barrierlessly generate the major product P1 HOSi++HCN and the minor one P3 HOSi++HNC, whereas other low-lying products such as P2 SiNCO++H2, and P0 H2NSi++CO are kinetically unfeasible. The high efficiency of the SiCN+/SiNC+ reaction towards H2O and the potential importance of SiCN+/SiNC+ ion chemistry in interstellar and SiCN-based microelectric and photoelectric processes strongly appeals for future laboratory investigations on the SiCN+/SiNC+ chemical reactivity. [ABSTRACT FROM AUTHOR]

This work predicts the extraordinary hyperpolarizability of inorganic clusters: two water trimer anions. The first hyperpolarizabilities of (H2O)3- are considerable, β0=1.715×107 a.u. for configuration A and β0=1.129×107 a.u. for configuration B at MP2/d-aug-cc-pVDZ+x level. The first hyperpolarizabilities of (H2O)3- (configuration A) and related systems [(H2O)3 and (H2O)3F-] are compared at the MP2/d-aug-cc-pVDZ+x level. These results are β0=1.715×107 a.u. for (H2O)3-, β0=35 a.u. for (H2O)3 [the neutral core of (H2O)3-], and β0=46 a.u. for (H2O)3F-. Comparing the β0 values of related systems, we find that the dipole-bound excess electron is the key factor in the extraordinary first hyperpolarizability of (H2O)3- species. It will provide a future in the development of some materials with the excess electron (e.g., electrides) that exhibit large nonlinear optical response. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

By the counterpoise-correlated potential energy surface method (interaction energy optimization), five structures of the C2H4-nFn-HF (n=0,1,2) dimers with all real frequencies have been obtained at MP2/aug-cc-pVDZ level. The influence of F substituent effect on the structure and π-hydrogen bond of dimer has been discussed. For C2H4-nFn-HF (n=1,2), the π-hydrogen bonds are elongated comparing with that for C2H4-HF. For C2H3F-HF, g-C2H2F2-HF, cis-C2H2F2-HF, the π-hydrogen bonds are further deformed. These changes (elongate, shift, and deformation) of π-hydrogen bond mainly come from deformation of π-electron cloud of C==C bond. The π-electron cloud is pushed towards the one C atom, the π H-bond shift also to the C direction. Since the two lobes of π-electron cloud have deviated slightly from the molecular vertical plane passing through C==C bond, the π-hydrogen bond is sloped. Intermolecular interaction energies of the dimers are calculated to be -3.9 for C2H4-HF, -2.8 for C2H3F-HF, -2.1 for g-C2H2F2-HF, -1.6 for cis-C2H2F2-HF, -1.3 kcal/mol for trans-C2H2F2-HF, at CCSD(T)/aug-cc-pVDZ level. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A dual-level direct dynamics study has been carried out for the two hydrogen abstraction reactions CF[sub 3]CHCl[sub 2]+Cl and CF[sub 3]CHFCl+Cl. The geometries and frequencies of the stationary points are optimized at the BHLYP/6-311G(d,p), B3LYP/6-311G(d,p), and MP2/6-31G(d) levels, respectively, with single-point calculations for energy at the BHLYP/6-311++G(3df,2p), G3(MP2), and QCISD(T)/6-311G(d,p) levels. The enthalpies of formation for the species CF[sub 3]CHCl[sub 2], CF[sub 3]CHFCl, CF[sub 3]CCl[sub 2], and CF[sub 3]CFCl are evaluated at higher levels. With the information of the potential energy surface at BHLYP/6-311++G(3df,2p)//6-311G(d,p) level, we employ canonical variational transition-state theory with small-curvature tunneling correction to calculate the rate constants. The agreement between theoretical and experimental rate constants is good in the measured temperature range 276–382 K. The effect of fluorine substitution on reactivity of the C–H bond is discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

By the counterpoise-correlated potential energy surface method (interaction energy optimization), the structure of the π H-bond complex FH...C[sub 4]H[sub 4]...HF has been obtained at the second-order Møller–Plesset perturbation theory (MP2/aug-cc-pVDZ) level. Intermolecular interaction energy of the complex is calculated to be -7.8 kcal/mol at the coupled-cluster theory with single, double substitutions and perturbatively linked triple excitations CCSD (T)/aug-cc-pVDZ level. The optimized structure is a “wheel with a pair of pedals” shaped (1|1) structure in which both HF molecules almost lie on either vertical line passing through the middle-point of the C==C bond on either side of the horizontal plane of the C[sub 4] ring for cyclobutadiene. In the structure, an antiaromatic ring π-dihydrogen bond is found, in which the proton acceptor is antiaromatic 4 electron and 4 center π bond and the donors are both acidic H atoms of HF molecules. In accompanying with the π-dihydrogen bond, two secondary interactions are exposed. The first is a repulsive interaction between an H atom of HF and a near pair of H atoms of C[sub 4]H[sub 4] ring. The second is the double π-type H bond between two lone pairs on a F atom and a far pair of H atoms. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ab initio direct dynamics methods have been used to study the title reaction. The electronic structure information including geometries, gradients and force constants (Hessians) is calculated at the QCISD/6-31+G(d) level. With the aid of intrinsic reaction coordinate theory, the minimum energy path (MEP) is obtained at the same level, and the energies along the MEP are further refined by performing the single-point calculations at the PMP4/6-311++G(3df,3pd) level. For this reaction, the theoretical rate constants by using improved canonical variational transition state theory incorporating small-curvature tunneling correction are in excellent agreement with the more recent experimental values. Our calculated results show that for the CH[sub 3]+HBr reaction, the rate constants have a strong nonlinear Arrhenius behavior, i.e., the CH[sub 3]+HBr reaction has negative temperature dependence at T<536 K, but clearly shows positive temperature dependence at T>536 K. The current work predicts that the kinetic isotope effect for the title reaction is normal in the temperature range 200–482 K, i.e., k[sub HBr]/k[sub DBr]>1. This result is in good agreement with the experimental one. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]