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Static and dynamic structures of water molecules have been inspected in aqueous solutions of di-and penta-α- and -β- d -glucopyranose (maltose, cellobiose, maltopentaose, and cellopentaose) outside the first hydration shell around the saccharides, using a molecular dynamics simulation which includes all degrees of freedom concerning atomic motion. The aim is to inspect the solute effect on water molecules in the aqueous solution systems corresponding to the length or the kind of the glycosidic linkage. We use the partial radial distribution function and two kinds of angular distribution functions for the static analysis, and find peculiarities in the solutions of both α-linked saccharides, maltose and maltopentaose. The broadness of the hydrogen bond network distribution in the maltose solution is particularly related to the translational motion of water molecules which is slowest in the maltose solution. The rotational motion of water molecules is significantly slow in the cellopentaose solution. The solute effect can be detected outside the first hydration shell around the solute, and is most noticeable in the translational motion.

A molecular dynamics simulation, which includes all degrees of freedom of atomic motion, has been carried out for aqueous maltose and cellobiose solutions in order to investigate whether the solvent as a background of solutes changes its dynamic characteristics or not. Mean square displacement, velocity autocorrelation function, rotational correlation function, and newly defined hydrogen bond correlation function have been calculated for the whole solvent from which the first hydration shell of the solute was omitted. The first three functions concern motions of each water molecule, and the last one reveals relative motions of water molecules. Translational and rotational motions of water molecules are restricted more in the solution than in the bulk water, because the network defects, which weaken the power of a water molecule to retain others, exist less in the solution than in the bulk water. Between two solution systems, this tendency is stronger in the maltose solution than in the cellobiose one. The difference between two solution systems is clearly demonstrated in the present study dealing with the dynamic structure, although it was not clear in the static structure revealed in our previous paper.

This paper, the first of a series of papers, examines equilibrium properties of N2O4⇌NO2 in liquid state by classical molecular dynamics simulations of liquid NO2. An ab initio MO calculation has been carried out to elucidate NO2–NO2 potential, and an orientation-sensitive pairwise potential (OSPP), which can reproduce highly anisotropic character of covalent bonding between N–N, has been formulated. The OSPP potential is parameterized by the well depth De and by two anisotropy factors: Aθ (0⩽Aθ⩽1) the anisotropy factor for the rocking angle between NN bond and ONO direction, and Aτ (0⩽Aτ⩽1) for torsional angle of the two NO2 about NN bond. The reactive liquid N2O4 is modeled as liquid NO2 which interacts with the OSPP potential between N–N atoms and Lennard-Jones potentials between N–O and O–O atoms. Equilibrium properties were found to be very sensitive to the well depth De and anisotropy factors of OSPP. The population of more than the NO2 dimer (3-mer, 4-mer,…) is considerable when anisotropy factors ...

A molecular dynamics (MD) simulation, which includes all degrees of freedom of atomic motion, has been carried out in order to investigate the temperature dependence of single particle dynamics such as translational and reorientational motions of liquid benzene (C 6 H 6 ). The translational diffusion coefficients D and first and second rank reorientational correlation times τ l R ( l =1, 2) of liquid C 6 H 6 are simulated at 366.12, 322.69, 295.00 and 198.54 K. Except for the simulation at 198.54 K, all three motions are characteristic of typical molecular liquids. Although these simulated D and τ l R values slightly deviate from experimental ones, both activation energies E a of simulated and experimental ones are in agreement with each other. The Stokes–Einstein–Debye (SED) equations, which are based on a hydrodynamics model, have also been checked for the D and τ l R values with changing temperature. It has been found that the SED equations hold for both values, and the hydrodynamical model is effective for the simulated liquid C 6 H 6 .

A molecular dynamics (MD) simulation, which includes all degrees of freedom of atomic motion, has been carried out in order to investigate the temperature dependence of single particle dynamics such as translational and reorientational motions of liquid carbon disulfide (CS 2 ). The translational diffusion coefficients D and first and second rank reorientational correlation times τ lr ( l = 1, 2) of liquid CS 2 are simulated at three temperatures. Both motions are characteristics of the typical molecular liquids, and these simulated D and τ lR values and the activation energies of them are close to the experimental ones. The Stokes-Einstein-Debye (SED) equations, which are based on a hydrodynamics model, have also been checked for the D and τ lR values with changing the temperature. It has been found that the SED equations hold for both values, and the hydrodynamical model is effective for the simulated liquid CS 2 .

We have applied our theory of the division of the viscosity B coefficient to the n-hexane-n-heptane, -n-octane, -n-decane, -n-undecane, and -n-dodecane systems at 25°C, and to the n-hexane-n-hexadecane system at 25, 45, 65, and 85 °C. Similar to the investigation of benzene regular solutions, a linear relation holds between the Bn term and the equimolar excess enthalpy HxaE = 0.5, and it has been clarified that the Bn term and the temperature coefficient of Bn for these systems are controlled by solute-solvent interaction.

A molecular dynamics (MD) simulation, which includes all degrees of freedom of atomic motion, has been carried out in order to investigate the temperature dependence of single particle dynamics such as translational and reorientational motions of liquid tetrachloromethane (CCl 4 ). The translational diffusion coefficients D and first and second rank reorientational correlation times τ lR ( l = 1, 2) of liquid CCl 4 are simulated at three temperatures. Both motions are characteristics of the typical molecular liquids, and these simulated D and τ lR values and their activation energies are close to the experimental ones. The Stokes-Einstein-Debye (SED) equations, which are based on a hydrodynamics model, have also been checked for the D and τ lR values with changing the temperatures. It has been found that the SED equations hold for both values, and the hydrodynamical model is effective for the simulated liquid CCl 4 .

Vibrational effects on structural parameters obtained by solid-state NMR are studied by theoretical calculations and molecular-dynamics simulations. The structural parameters treated contain internuclear distances between directly bonded or remote nuclei including nonproton pairs in a molecule and bond and dihedral angles. In addition to the intramolecular normal mode vibrations, the libration of the whole molecule is considered in the theory. It is shown that the molecular libration as well as the intramolecular vibrations reduce dipolar interactions, and consequently lengthen the internuclear distances obtained from the dipolar interactions (RNMR). In contrast, the internuclear distances obtained by single crystal x-ray or neutron diffraction (Rcor) are proved to be shortened by the molecular libration. Molecular-dynamics simulations for glycine molecules in the crystal at room temperature reveal that RNMR are 1%–4% longer than Rcor, confirming the theoretical results. It is also demonstrated that the e...

Molecular dynamics simulations were performed for the dissociation and association (D/A) reactions N 2 O 4 2NO 2 in the gas and liquid phases. The transition state of the D/A reactions was identified as the phase space surface E T =0, where E T is the sum of the potential and kinetic energies of the interfragment motion. The dissociation reaction in liquid N 2 O 4 is found to occur by two steps: first, a reactant is activated by intermolecular energy transfer from solvent to reactant, and second, the dissociation occurs by energy transfer from intrafragment vibrational and rotational modes to interfragment translational mode. The association reaction proceeds by two steps: interfragment translational energy of an encounter NO 2 pair is transferred to intrafragment modes and then the associated N 2 O 4 is deactivated by intermolecular energy transfer from product to solvent.

In order to explain the large permittivity of liquid cyanogen consisting of centrosymmetric molecules, a molecular dynamics simulation which includes all degrees of freedom of vibration, rotation, and translation has been performed. The intramolecular potential energy is expressed in terms of the internal coordinates with quadratic, cubic, and quartic force constants. The intermolecular potential consists of an atom–atom pair potential with Coulombic and Buckingham terms. The simulation has given an adequate value of self‐diffusion coefficient and a typical form of radial distribution function for the liquid state. The simulation has reproduced well the large value of the permittivity observed in experiments, suggesting that the value results from the extraordinarily large atomic polarization brought by the intramolecular bending motion in an antisymmetric mode. The simulation has also suggested that the nitrogen atoms collide with each other more frequently than with carbon atoms and the collision shifts the normal frequencies related to the N≡C bond to higher frequency. The infrared and Raman spectra together with the real and imaginary parts of the refractive index have also been calculated.

Molecular dynamics simulations were performed for the dissociation and association (D/A) reactions N2O4■2 NO2 in the gas phase and in liquid N2O4. The trajectory was initialized from an equilibrium distribution of all variables in liquid N2O4, except the reactive mode, the NN distance of a reactant NO2 pair, was excited above the dissociation limit of the Morse‐like potential between NO2 fragments, and the dynamics were calculated for 500 fs both forward and backward in time. Characteristics of the translational and vibrational energy relaxations of the reactant were studied in detail. Energy ERT, which is defined to be the sum of the potential and kinetic energies of interfragment motion, is found to play a key role in the D/A dynamics; a reactant pair is associated when ERT

In order to study the cation dependence of the ionic dynamics in molten nitrates, molecular dynamics simulations including vibrational degrees of freedom were carried out for molten LiNO3, NaNO3, and RbNO3. Coulomb pair potential with Born‐type repulsion was adopted for the interionic interaction. The simulated diffusion coefficient was smaller for a larger cation, and that of nitrate ions did not change with changing cation species. The mean squared charge displacements showed that the static conductivity decreased considerably as the cation size increased from Li+ to Rb+. The simulated orientational correlation function of nitrate ions decayed more quickly as the cation size increased. Far infrared absorption spectrum simulated from the time evolution of the dipole moment (or the current) of the system showed that the peak shifted to the low energy side and the intensity decreased as the cation size increased. Results of the simulation were compared with the experimental diffusion constants, static and ...

To study the microdynamics of translational, orientational and vibrational motions in liquid N2O4, molecular dynamics simulations, including all degrees of freedom of vibrating N2O4 molecules, were carried out. Atom-atom Lennard-Jones potentials with and without Coulomb potentials (LJ + C and LJ, respectively), were adopted in the simulation. When Coulomb interaction between atoms was included, mean-squared force and torque increased, the velocity and angular momentum correlation functions decayed faster to more evident negative parts, and both the translational and orientational diffusion slowed down. Simulated rotational correlation functions for LJ + C agreed reasonably with those derived from Raman spectroscopy, while those for LJ were found to decay too fast. Vibrational correlation functions for the NN stretching v 3 mode were calculated and the vibrational spectra were obtained from their Fourier transforms. Two simulations for the harmonic and the anharmonic intramolecular potentials, where anharm...

Molecular dynamics simulation has been used to investigate the infrared spectra of ordered and disordered benzoic acid crystals consisting of various proportions of the A and B configurations, whose C–O and C=O bonds are approximately parallel to the a axis, respectively. The simulation reproduced well the splitting and the temperature dependence in intensity for the C=O stretching bands observed. The absorption coefficient of the lower frequency band was simulated as several times larger than that of the higher frequency band in accord with the observed. To interpret this peculiar result of the molecular dynamics simulation, a simple calculation of the band splitting has been made in terms of the transition dipole–transition dipole interaction. It has been shown that the interaction is an essential factor to produce the large difference in intensity and the splitting for the C=O stretching bands. The higher and lower bands are interpreted as due to the A configuration reduced in intensity by the B form, and due to the B form enhanced in intensity by the A form, respectively. Compression effect in the O⋅⋅⋅O distance of the hydrogen bond is also studied in comparison with the observed value.

In order to study the effect of the potential well on the single ion dynamics and the charge transport in molten LiNO3, a molecular dynamics simulation, which included all degrees of freedom of vibrating nitrate ions, was carried out. Simple Coulomb pair potential with Born‐type repulsion was adopted as a standard, and a potential well of varying depth between Li+ and O of NO−3 was added to the standard potential. As the well depth increased, both the translational and orientational diffusion were found to slow down, leading to solid like dynamics. The potential dependence of the ionic dynamics was studied from the translational, orientational, and current correlation functions. Results of the simulation were compared with the experimental diffusion constants, static conductivity, and rotational behavior revealed by Raman spectroscopy. Using the relation between the infrared absorption spectrum and the autocorrelation function of the dipole moment (or the current) of the system, we carried out the first s...

The fluorescence spectrum for the 4S 3 2 → 4I 15 2 transition of the erbium ethylsulfate crystal has been observed at 87 K by using the 488.0 nm line of an Ar+ laser. According to the Judd—Ofelt theory for spectral intensity, the relative intensities of 10 σ transitions and 5π transitions between the manifolds have been evaluated using wavefunctions obtained from a crystalfield calculation including configuration interaction. The calculated intensities are in fair agreement with experiment. A discussion is given of the approximations employed.

The microdynamics of orientational motion (the tumbling of the symmetry axis and the spinning about the axis) of nitrate ions has been investigated in a molecular dynamics simulation of molten LiNO3. Simple Coulomb potential with Born type repulsion has been adopted and all degrees of freedom of vibrating nitrate ions have been included in the simulation. The relaxation of the orientational correlation functions is studied in the cumulant expansion scheme, and a correlation function which reflects only the spinning motion is separated by the method of Lynden‐Bell et al. It is found that the angular momentum correlation function for the perpendicular component C⊥J(t) has a pronounced negative portion, which is clear evidence of librations in a temporary solvent cage. C∥J(t) has a shallow negative lobe. The spinning motion is less hindered and the reorientation is faster. Both the tumbling and the spinning motions are found to be predominantly Markovian. The difference between the tumbling and the spinning ...

The I.R. spectra of benzoic acid crystal composed of the A configuration were simulated using the method of molecular dynamics, where all degrees of freedom of vibration, rotation and translation were taken into account and the equilibrium charge and charge fluxes were employed in the formulation. The observed spectra were reproduced satisfactorily, and the crystal field effect considered in the simulation led to reasonable shifts of respective frequencies from those calculated by the normal coordinate analysis for an isolated dimer. The most remarkable shifts were observed in the OH stretching (ca. 200 cm−1) and the OH out-of-plane bending (61 cm−1) modes. Far infrared spectra were also obtained in the simulation. The compression of the O … O distance due to the crystal field effect was found to be between 0·04 and 0·05 A which agreed well with the experimental result.

In order to study the microdynamics of translational and orientational motion of ions in liquid electrolytes, a molecular dynamics simulation of molten LiNO3, which includes all degrees of freedom of vibrating nitrate ions, has been performed. Simple Coulomb pair potentials with Born‐type repulsions have been adopted in the simulation. The calculated properties include: translational velocity and force correlation functions, rotational correlation functions, and angular momentum and torque correlation functions. The nature of the ionic motion is analyzed in terms of quasioscillation and quasilibration. Local structures surrounding nitrate ions, which can be characterized by, e.g., the coordination number, are found to persist for a long time (∼1 ps). The coupling between the environmental structure and the translational and orientational behaviors of a given nitrate ion has been examined through selectively sampled correlation functions. We found that the change of coordination number enhances the transla...

Etude theorique de la hauteur de la barriere de potentiel pour un double transfert de proton, apres optimisation de la geometrie C 2h (equilibre) et D 2h (etat de transition), avec un ensemble de base 4-31G ou apres interaction de configurations avec des ensembles de base 4-31G ou 5-31G **