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Equimolar mixtures of glymes and organic lithium salts are known to produce solvate ionic liquids, in which the stability of the [Li(glyme)]+ complex plays an important role in determining the ionic dynamics. Since these mixtures have attractive physicochemical properties for application as electrolytes, it is important to understand the dependence of the stability of the [Li(glyme)]+ complex on the ion dynamics. A series of microsecond molecular dynamics simulations has been conducted to investigate the dynamic properties of these solvate ionic liquids. Successful solvate ionic liquids with high stability of the [Li(glyme)]+ complex have been shown to have enhanced ion dynamics. Li-glyme pair exchange rarely occurs: its characteristic time is longer than that of ion diffusion by one or two orders of magnitude. Li-glyme pair exchange most likely occurs through cluster formation involving multiple [Li(glyme)]+ pairs. In this process, multiple exchanges likely take place in a concerted manner without the production of energetically unfavorable free glyme or free Li+ ions. [ABSTRACT FROM AUTHOR]

Room temperature ionic liquids (ILs) are stable liquids composed of anions and cations. 1-ethyl-3-methyl-imidazolium (EMIm, EMI) is a popular and important cation that produces thermally stable ILs with various anions. In this study two amide-type anions, bis(trifluoro-methanesulfonyl)amide [N(SO2CF3)2, TFSA, TFSI, NTf2, or Tf2N] and bis(fluorosulfonyl)amide [(N(SO2F)2, FSA, or FSI] were investigated by multinuclear NMR spectroscopy. In addition to EMIm-TFSA and EMIm-FSA, lithium-salt-doped binary systems were prepared (EMIm-TFSA-Li and EMIm-FSA-Li). The spin-lattice relaxation times (T1) were measured by 1H, 19F, and 7Li NMR spectroscopy and the correlation times of 1H NMR, τc(EMIm) (8 × 10-10 to 3 × 10-11 s) for the librational molecular motion of EMIm and those of 7Li NMR, τc(Li) (5 × 10-9 to 2 × 10-10 s) for a lithium jump were evaluated in the temperature range between 253 and 353 K. We found that the bulk viscosity (η) versus τc(EMIm) and cation diffusion coefficient DEMIm versus the rate 1/τc(EMIm) have good relationships. Similarly, linear relations were obtained for the η versus τc(Li) and the lithium diffusion coefficient DLi versus the rate 1/τc(Li). The mean one-jump distances of Li were calculated from τc(Li) and DLi. The experimental values for the diffusion coefficients, ionic conductivity, viscosity, and density in our previous paper were analyzed by the Stokes-Einstein, Nernst-Einstein, and Stokes-Einstein-Debye equations for the neat and binary ILs to clarify the physicochemical properties and mobility of individual ions. The deviations from the classical equations are discussed. [ABSTRACT FROM AUTHOR]

Room-temperature ionic liquids (RTIL, IL) are stable liquids composed of anions and cations. N-methyl-N-propyl-pyrrolidinium (P13, Py13, PYR13, or mppy) is an important cation and produces stable ILs with various anions. In this study two amide-type anions, bis(trifluoromethanesulfonyl)amide [N(SO2CF3)2, TFSA, TFSI, NTf2, or Tf2N] and bis(fluorosulfonyl)amide [N(SO2F)2, FSA, or FSI], were investigated. In addition to P13-TFSA and P13-FSA, lithium salt doped samples were prepared (P13-TFSA-Li and P13-FSA-Li). The individual ion diffusion coefficients (D) and spin-lattice relaxation times (T1) were measured by 1H, 19F, and 7Li NMR. At the same time, the ionic conductivity (σ), viscosity (η), and density (ρ) were measured over a wide temperature range. The van der Waals volumes of P13, TFSA, FSA, Li(TFSA)2, and Li(FSA)3 were estimated by molecular orbital calculations. The experimental values obtained in this study were analyzed by the classical Stokes-Einstein, Nernst-Einstein (NE), and Stokes-Einstein-Debye equations and Walden plots were also made for the neat and binary ILs to clarify physical and mobile properties of individual ions. From the temperature-dependent velocity correlation coefficients for neat P13-TFSA and P13-FSA, the NE parameter 1-ξ was evaluated. The ionicity (electrochemical molar conductivity divided by the NE conductivity from NMR) and the 1-ξ had exactly the same values. The rotational and translational motions of P13 and jump of a lithium ion are also discussed. [ABSTRACT FROM AUTHOR]

The CCSD(T) level interaction energies of eight orientations of nitrobenzene-benzene complexes and nine orientations of nitrobenzene dimers at the basis set limit have been estimated. The calculated interaction energy of the most stable slipped-parallel (Cs) nitrobenzene-benzene complex was -4.51 kcal/mol. That of the most stable slipped-parallel (antiparallel) (C2h) nitrobenzene dimer was -6.81 kcal/mol. The interaction energies of these complexes are significantly larger than that of the benzene dimer. The T-shaped complexes are substantially less stable. Although nitrobenzene has a polar nitro group, electrostatic interaction is always considerably weaker than the dispersion interaction. The dispersion interaction in these complexes is larger than that in the benzene dimer, which is the cause of the preference of the slipped-parallel orientation in these complexes. [ABSTRACT FROM AUTHOR]

The MP2 (the second-order Mo\ller-Plesset calculation) and CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energies of all-trans n-alkane dimers were calculated using Dunning's [J. Chem. Phys. 90, 1007 (1989)] correlation consistent basis sets. The estimated MP2 interaction energies of methane, ethane, and propane dimers at the basis set limit [EMP2(limit)] by the method of Helgaker et al. [J. Chem. Phys. 106, 9639 (1997)] from the MP2/aug-cc-pVXZ (X=D and T) level interaction energies are very close to those estimated from the MP2/aug-cc-pVXZ (X=T and Q) level interaction energies. The estimated EMP2(limit) values of n-butane to n-heptane dimers from the MP2/cc-pVXZ (X=D and T) level interaction energies are very close to those from the MP2/aug-cc-pVXZ (X=D and T) ones. The EMP2(limit) values estimated by Feller's [J. Chem. Phys. 96, 6104 (1992)] method from the MP2/cc-pVXZ (X=D, T, and Q) level interaction energies are close to those estimated by the method of Helgaker et al. from the MP2/cc-pVXZ (X=T and Q) ones. The estimated EMP2(limit) values by the method of Helgaker et al. using the aug-cc-pVXZ (X=D and T) are close to these values. The estimated EMP2(limit) of the methane, ethane, propane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane dimers by the method of Helgaker et al. are -0.48, -1.35, -2.08, -2.97, -3.92, -4.91, -5.96, -6.68, -7.75, and -8.75 kcal/mol, respectively. Effects of electron correlation beyond MP2 are not large. The estimated CCSD(T) interaction energies of the methane, ethane, propane, and n-butane dimers at the basis set limit by the method of Helgaker et al. (-0.41, -1.22, -1.87, and -2.74 kcal/mol, respectively) from the CCSD(T)/cc-pVXZ (X=D and T) level interaction energies are close to the EMP2(limit) obtained using the same basis sets. The estimated EMP2(limit) values of the ten dimers were fitted to the form m0+m1X (X is 1 for methane, 2 for ethane, etc.). The obtained m0 and m1 (0.595 and -0.926 kcal/mol) show that the interactions between long n-alkane chains are significant. Analysis of basis set effects shows that cc-pVXZ (X=T, Q, or 5), aug-cc-pVXZ (X=D, T, Q, or 5) basis set, or 6-311G** basis set augmented with diffuse polarization function is necessary for quantitative evaluation of the interaction energies between n-alkane chains. [ABSTRACT FROM AUTHOR]

The intermolecular interaction energy of the toluene dimer has been calculated with the ARS-F model (a model chemistry for the evaluation of intermolecular interaction energy between ARomatic Systems using Feller’s method), which was formerly called as the AIMI model III. The CCSD(T) (coupled cluster calculations with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the second-order Mo\ller–Plesset perturbation interaction energy at the basis set limit obtained by Feller’s method and the CCSD(T) correction term obtained using a medium-size basis set. The cross (C2) dimer has the largest (most negative) interaction energy (-4.08 kcal/mol). The antiparallel (C2h) and parallel (CS) dimers (-3.77 and -3.41 kcal/mol, respectively) are slightly less stable. The dispersion interaction is found to be the major source of attraction in the toluene dimer. The dispersion interaction mainly determines the relative stability of the stacked three dimers. The electrostatic interaction of the stacked three dimers is repulsive. Although the T-shaped and slipped-parallel benzene dimers are nearly isoenergetic, the stacked toluene dimers are substantially more stable than the T-shaped toluene dimer (-2.62 kcal/mol). The large dispersion interaction in the stacked toluene dimers is the cause of their enhanced stability. [ABSTRACT FROM AUTHOR]

Intermolecular interaction energies of 12 orientations of C3F8 dimers were calculated with electron correlation correction by the second-order Møller-Plesset perturbation method. The antiparallel C2h dimer has the largest interaction energy (-1.45 kcal/mol). Electron correlation correction increases the attraction considerably. Electrostatic energy is not large. Dispersion is mainly responsible for the attraction. Orientation dependence of the interaction energy of the C3F8 dimer is substantially smaller than that of the C3H8 dimer. The calculated interaction energy of the C3F8 dimer at the potential minimum is 78% of that of the C3H8 dimer (-1.85 kcal/mol), whereas the interaction energies of the CF4 and C2F6 dimers are larger than those of the CH4 and C2H6 dimers. The intermolecular separation in the C3F8 dimer at the potential minimum is substantially larger than that in the C3H8 dimer. The larger intermolecular separation due to the steric repulsion between fluorine atoms is the cause of the smaller interaction energy of the C3F8 dimer at the potential minimum. The calculated intermolecular interaction energy potentials of the C3F8 dimers using an all atom model OPLS-AA (OPLS all atom model) force field and a united atom model force field were compared with the ab initio calculations. Although the two force fields well reproduces the experimental vapor and liquid properties of perfluoroalkenes, the comparison shows that the united atom model underestimates the potential depth and orientation dependence of the interaction energy. The potentials obtained by the OPLS-AA force field are close to those obtained by the ab initio calculations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The intermolecular interaction energies of naphthalene dimers have been calculated by using an aromatic intermolecular interaction model (a model chemistry for the evaluation of intermolecular interactions between aromatic molecules). The CCSD(T) (coupled cluster calculations with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the second-order Møller–Plesset perturbation interaction energy near saturation and the CCSD(T) correction term obtained using a medium-size basis set. The estimated interaction energies of the set of geometries explored in this work show that two structures emerge as being the lowest energy, and may effectively be considered as isoenergetic on the basis of the errors inherent in out extrapolation procedure. These structures are the slipped-parallel (C[sub i]) structure (-5.73 kcal/mol) and the cross (D[sub 2d]) structure (-5.28 kcal/mol). The T-shaped (C[sub 2v]) and sandwich (D[sub 2h]) dimers are substantially less stable (-4.34 and -3.78 kcal/mol, respectively). The dispersion interaction is found to be the major source of attraction in the naphthalene dimer. The electrostatic interaction is substantially smaller than the dispersion interaction. The large dispersion interaction is the cause of the large binding energies of the cross and slipped-parallel dimers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The π/π interaction (stacking) and N(B)–H/π interaction of the borazine (B[sub 3]N[sub 3]H[sub 6]) dimer were theoretically studied. In contrast to the benzene dimer, the gauche parallel-stacked dimer of borazine was energetically minimum, and total interaction energy was about 1 kcal/mol more negative than that of the parallel-stacked dimer of benzene. The gauche parallel-stacked dimer of borazine was more stable than slipped parallel-stacked dimers and T-shape dimers. The syn parallel-stacked dimer of borazine was energetically unstable and it was less stable than the slipped syn parallel-stacked structures. The electron correlation effect at higher than the second-order Møller–Plesset (MP2) level on the molecular interaction energy was quite small. The dispersion term and the charge transfer term had large contribution in almost all the borazine dimer formations, except the syn parallel-stacked dimer. In the case of syn parallel-stacked dimer, contribution of the dispersion term was dominant. The electrostatic term had only small contribution for all the dimer formations. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The energy profile of the interconversion path between the T-shape and slipped-parallel dimers has been studied by high level ab initio calculations. The CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the MP2 (the second-order Møller-Plesset calculation) interaction energy near the basis set limit and the CCSD(T) correction term using the 6-311G[sup *] basis set. The calculated CCSD(T) level energy profile has shown that the potential is very flat and the interconversion barrier height is very small (around 0.2 kcal/mol). The MP2 calculations using large basis sets near the basis set limit considerably overestimate the attraction of the slipped-parallel dimer, which indicates the importance of higher level electron correlation correction for studying the potential energy surface of the benzene dimer. [ABSTRACT FROM AUTHOR]

Intermolecular interaction energies of eight orientation CF[sub 4] dimers and seven orientation C[sub 2]F[sub 6] dimers were calculated with electron correlation correction by the second-order Moller-Plesset perturbation (MP2) method. The D[sub 3d] CF[sub 4] dimer and C[sub 2h] C[sub 2]F[sub 6] dimer have the largest binding energies. Electron correlation correction increases the attraction considerably, while the effects of electron correlation beyond MP2 are small. Electrostatic and induction energies are not large in all cases. This indicates that dispersion interaction is mainly responsible for the attraction. The calculated binding energy of the CF[sub 4] dimer (0.69 kcal/mol) is about 60% larger than that of the CH[sub 4] dimer (0.44 kcal/mol), while the binding energy of the C[sub 2]F[sub 6] dimer (1.02 kcal/mol) is close to that of the C[sub 2]H[sub 6] dimer (0.90 kcal/mol). The intermolecular separations (C···C distance) in the CF[sub 4] and CH[sub 4] dimers at the potential minima are close (4.0 and 3.8 Å, respectively), while the separation in the C[sub 2]F[sub 6] dimer (4.8 Å) is appreciably larger than that in the C[sub 2]H[sub 6] dimer (4.0 Å). The larger intermolecular separation in the C[sub 2]F[sub 6] dimer reduces dispersion energy. Therefore the binding energies of the C[sub 2]F[sub 6] and C[sub 2]F[sub 6] dimers are not largely different. The molar volume of C[sub 2]F[sub 6] is substantially larger than that of C[sub 2]F[sub 6] due to bulky fluorine atoms. The small difference of the binding energies suggests that the large molecular volume of perfluoroalkanes is the cause of their small heats of vaporization per volume. [ABSTRACT FROM AUTHOR]

Studies the effects of basis set and electron correlation on the calculated interaction energies of hydrogen bonding complexes. Use of the Dunning's correlation consistent basis sets in the study; Effects of electron correlation; Effects of basis set; Interaction energies at the basis-set limit.

Calculates the internal rotational barrier heights of biphenyl with the Dunning correlation consisted basis sets and the electron correlation correction by the second order Moller-Plesset method. Calculations of benzene dimers suggesting that the dispersion interaction increased the relative stability of the coplanar conformer.

Investigates the intermolecular interaction potential of the carbon dioxide dimer. Absence of an inversion barrier; Calculation of the energy difference of the dimer; Use of diffuse polarization in evaluating the essential attractive interactions.

The stabilization energies for the formation (Eform) of 11 ion pairs of protic and aprotic ionic liquids were studied by MP2/6-311G** level ab initio calculations to elucidate the difference between the interactions of ions in protic ionic liquids and those in aprotic ionic liquids. The interactions in the ion pairs of protic ionic liquids (diethylmethylammonium [dema] and dimethylpropylammonium [dmpa] based ionic liquids) are stronger than those of aprotic ionic liquids (ethyltrimethylammonium [etma] based ionic liquids). The Eform for the [dema][CF3SO3] and [dmpa][CF3SO3] complexes (-95.6 and -96.4 kcal/mol, respectively) are significantly larger (more negative) than that for the [etma][CF3SO3] complex (-81.0 kcal/mol). The same trend was observed for the calculations of ion pairs of the three cations with the Cl-, BF4-, TFSA- anions. The anion has contact with the N-H bond of the dema+ or dmpa+ cations in the most stable geometries of the dema+ and dmpa+ complexes. The optimized geometries, in which the anions locate on the counter side of the cations, are 11.0-18.0 kcal/mol less stable, which shows that the interactions in the ions pairs of protic ionic liquids have strong directionality. The Eform for the less stable geometries for the dema+ and dmpa+ complexes are close to those for the most stable etma+ complexes. The electrostatic interaction, which is the major source of the attraction in the ion pairs, is responsible for the directionality of the interactions and determining the magnitude of the interaction energy. Molecular dynamic simulations of the [dema][TFSA] and [dmpa][TFSA] ionic liquids show that the N-H bonds of the cations have contact with the negatively charged (oxygen and nitrogen) atoms of TFSA- anion, while the strong directionality of the interactions was not suggested from the simulation of the [etma][CF3SO3] ionic liquid. [ABSTRACT FROM AUTHOR]

The performance of density functional theory using the Perdew and Wang's exchange and correlation functionals (PW91) functional for the prediction of intermolecular interaction energies is evaluated based on calculations on the neon, argon, methane, ethylene, and benzene dimers, as well as on 12 hydrogen bonded complexes (water, methanol, formic acid, hydrogen fluoride, ammonia, formamide dimers and water-methanol, water-dimethyl ether, water-formaldehyde, hydrogen cyanide-hydrogen fluoride, water-ammonia, water-formamide complexes). The results were compared with those obtained from Becke's exchange and Lee, Yang, and Parr's correlation functionals (BLYP), Becke's 3 parameter functional combined with Lee, Yang, and Parr's correlation functional (B3LYP), second order Mo\ller-Plesset perturbation (MP2), and coupled cluster calculations with single and double substitutions and with non-iterative triple corrections [CCSD(T)] calculations. The calculated interaction energies show that the PW91 functional performs much better than the BLYP or B3LYP functionals. The error in the computed binding energies of the hydrogen bonded complexes is 20% in the worst case. The most demanding cases are the systems with large dispersion contributions to the binding energy, such as the benzene dimer. In contrast to the BLYP and B3LYP functionals which fail to account for dispersion, the PW91 functional at least partly recovers the attraction. The basis set dependence of the PW91 functionals is relatively small in contrast to the MP2 and CCSD(T) methods. Despite its occasional difficulties with dispersion interaction, the PW91 functional may be a viable alternative to the ab initio methods, certainly in situations where large complexes are being studied. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Equimolar mixtures of glymes and organic lithium salts are known to produce solvate ionic liquids, in which the stability of the [Li(glyme)] + complex plays an important role in determining the ionic dynamics. Since these mixtures have attractive physicochemical properties for application as electrolytes, it is important to understand the dependence of the stability of the [Li(glyme)] + complex on the ion dynamics. A series of microsecond molecular dynamics simulations has been conducted to investigate the dynamic properties of these solvate ionic liquids. Successful solvate ionic liquids with high stability of the [Li(glyme)] + complex have been shown to have enhanced ion dynamics. Li-glyme pair exchange rarely occurs: its characteristic time is longer than that of ion diffusion by one or two orders of magnitude. Li-glyme pair exchange most likely occurs through cluster formation involving multiple [Li(glyme)] + pairs. In this process, multiple exchanges likely take place in a concerted manner without the production of energetically unfavorable free glyme or free Li + ions.

Intermolecular interactions in the crystals of tetra- and penta-thienoacene were studied using ab initio molecular orbital calculations for evaluating the magnitude of characteristic S⋯S interactions with great attention paid to their origin. The interactions between the π-stacked neighboring molecules are significantly greater than those between the neighboring molecules exhibiting the S⋯S contact, although it has sometimes been claimed that the S⋯S interactions play important roles in adjusting the molecular arrangement of sulfur-containing polycyclic aromatic molecules in the crystals owing to short S⋯S contacts. The coupled cluster calculations with single and double substitutions with noniterative triple excitation interaction energies at the basis set limit estimated for the π-stacked and S⋯S contacted neighboring molecules in the tetrathienoacene crystal are -11.17 and -4.27 kcal/mol, respectively. Those for π-stacked molecules in the pentathienoacene crystal is -14.38 kcal/mol, while those for S⋯S contacted molecules are -7.02 and -6.74 kcal/mol. The dispersion interaction is the major source of the attraction between the π-stacked and S⋯S contacted molecules, while the orbital-orbital interactions are repulsive: The orbital-orbital interactions, which are significant for charge carrier transport properties, are not much more than the results of the short S⋯S contact caused by the strong dispersion interactions. Besides, the intermolecular interaction energy calculated for a trithienoacene dimer has strong orientation dependence.

Room-temperature ionic liquids (RTIL, IL) are stable liquids composed of anions and cations. N-methyl-N-propyl-pyrrolidinium (P(13), Py(13), PYR(13), or mppy) is an important cation and produces stable ILs with various anions. In this study two amide-type anions, bis(trifluoromethanesulfonyl)amide [N(SO(2)CF(3))(2), TFSA, TFSI, NTf(2), or Tf(2)N] and bis(fluorosulfonyl)amide [N(SO(2)F)(2), FSA, or FSI], were investigated. In addition to P(13)-TFSA and P(13)-FSA, lithium salt doped samples were prepared (P(13)-TFSA-Li and P(13)-FSA-Li). The individual ion diffusion coefficients (D) and spin-lattice relaxation times (T(1)) were measured by (1)H, (19)F, and (7)Li NMR. At the same time, the ionic conductivity (σ), viscosity (η), and density (ρ) were measured over a wide temperature range. The van der Waals volumes of P(13), TFSA, FSA, Li(TFSA)(2), and Li(FSA)(3) were estimated by molecular orbital calculations. The experimental values obtained in this study were analyzed by the classical Stokes-Einstein, Nernst-Einstein (NE), and Stokes-Einstein-Debye equations and Walden plots were also made for the neat and binary ILs to clarify physical and mobile properties of individual ions. From the temperature-dependent velocity correlation coefficients for neat P(13)-TFSA and P(13)-FSA, the NE parameter 1-ξ was evaluated. The ionicity (electrochemical molar conductivity divided by the NE conductivity from NMR) and the 1-ξ had exactly the same values. The rotational and translational motions of P(13) and jump of a lithium ion are also discussed.