Molecular ordering of a cyano compound at a displacive transition temperature: a statistical analysis based on quantum mechanics and computer simulations

A statistical analysis has been carried out to determine the configurational preference of a pair of 4-cyanophenyl 4-n-pentylbenzoate (CPPB) molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. Configurational energy has been computed using the Rayleigh—Schodinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at the phase transition temperature using the Maxwell—Boltzmann formula. An attempt has been made to identify the most probable configuration at the phase transition temperature. Further, the flexibility of various configurations has been studied in terms of variation of probability due to small departures from the most probable configuration. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of the molecular pair have been considered. The results are discussed in the light of experimental as well as theoretical observations. The nature of the mesophase has been correlated with the parameter introduced in this paper.     

Ordering of fluoro-mesogens: a statistical approach based on quantum mechanics and computer simulation

Computational analysis of the molecular ordering of nematic p -phenylene-4-methoxy benzoyl 4-trifluoromethylbenzoate (FLUORO1) and smectic 4-propyloxyphenyl 4-(4-trifluoromethylbenzoyloxy) benzoate (FLUORO2) mesogens has been carried out with respect to translatory and orientational motions. The net atomic charge and atomic dipole components at each atomic centre of the molecule have been evaluated using the CNDO/2 method. Rayleigh-Schrodinger perturbation theory, along with the multicentred-multipole expansion method, has been employed to evaluate long range intermolecular interactions while a '6-exp' potential function has been assumed for short range interactions. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at the phase transition temperature using the Maxwell-Boltzmann formula. The flexibility of various configurations has been studied in terms of the variation of probability due to small departures from the most probable configuration. The results obtained enable the determination of the peculiarities of the molecular ordering, as well as the construction of models of the structures of FLUORO1 and FLUORO2 in different modes of interaction. The mesophase nature has been correlated with the parameters introduced in this paper.     

Ordering of a monotropic nematic liquid crystal in dielectric medium at phase transition temperature: A computational analysis

Ordering in a monotropic nematic liquid crystal, 4’-n-butyl-4-cyanobiphenyl, was examined by the methods of quantum mechanics and intermolecular forces. The atomic charges and dipole moment at each atomic center were evaluated by the CNDO/2 method. The configurational energy was computed using the Rayleigh-Schrödinger perturbation method. The total interaction energies obtained by these computations were used to calculate the probability of each configuration in a dielectric medium (noninteracting and nonmessogenic solvent, benzene) at the phase transition temperature using the Maxwell-Boltzmann formula. In the dielectric medium, the energies/probabilities are redistributed, and there is a considerable rise in the probability of interactions, although the order of preference remains the same. An attempt was made to develop a new and interesting model of nematogen in a dielectric medium. A theoretical support is offered to the experimental observations.     

Molecular organization of 4-cyano-4′-nonylbiphenyl in a dielectric medium: A statistical analysis

The molecular organization of 4-cyano-4′-nonylbiphenyl (CNBP) in a dielectric medium has been explored using a statistical model based on quantum mechanics and computer simulation. The complete neglect differential overlap (CNDO/2) method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. The modified Rayleigh-Schrodinger perturbation theory along with multicentered multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while the 6-exp potential function has been assumed for short-range interactions. The total interaction energies obtained through these computations were used as input to calculate the probability of occurrence of each configuration in a dielectric medium, benzene, at room temperature (300 K) using the MB formula. The various possible geometrical arrangements between a molecular pair during the different modes of interactions have been considered. This provides theoretical support to the experimental observations.     

Ordering of thermotropic nematogen in dielectric medium — a computational analysis

A computational analysis of ordering in homologous series of 4-cyano-4′-alkylbiphenyls (nCB) with alkyl group heptyl (7CB) has been carried out with respect to translatory and orientational motions. The complete neglect differential overlap (CNDO/2) method was employed to evaluate the net atomic charge and atomic dipole components at each atomic center of the molecule. The modified Rayleigh-Schrödinger perturbation theory along with multicentered-multipole expansion method was employed to evaluate the long-range intermolecular interactions, while 6-exp potential function was assumed for short-range interactions. The total interaction energy values obtained through these computations were used as input to calculate the probability of each configuration in non-interacting and non-mesogenic solvent (i.e., benzene) at room temperature (300 K) using the Maxwell-Boltzmann formula. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of molecular pairs were considered and the most favorable configuration of pairing was obtained. The present article offers theoretical support to the experimental findings.     

Computer simulation of molecular organization in a nematogen. The role of thermodynamic parameters

Computer simulations of molecular organization in a nematogen, alkenyl bicyclohexylnitrile (ALBCHNL), have been carried out with respect to translational and orientational motions. The atomic net charge and dipole moment at each atomic center has been evaluated using the complete neglect of differential overlap (CNDO/2) method. The modified Rayleigh-Schroedinger perturbation theory, along with multicentered-multipole expansion method, has been employed to evaluate long-range intermolecular interactions, while a “6-exp” potential function has been assumed for short-range interactions. The total interaction energy values obtained through these computations have been used as input to calculate the thermodynamical parameters such as entropy and Helmholtz free energy of each configuration at room temperature (300 K), nematic-isotropic transition (364.7 K) and above transition temperature (450 K). An attempt has been made to understand the molecular organization, to develop a new and interesting model for nematogen based on the thermodynamic parameters introduced in this article.     

金属Cu液固转变及晶体生长的分子动力学模拟

采用分子动力学模拟研究了液态Ｃｕ在不同冷却速度下的凝固特点,模拟采用ＥＡＭ作用势,计算了不同温度,不同冷却速度下Ｃｕ的偶相关函数,结果表明ＥＡＭ作用势能很好地描述液态Ｃｕ的结构特征,当冷却速度较快时,液Ｃｕ形成非晶;当冷却速度较慢时,液Ｃｕ形成晶体,分析了不同冷却速度下体系的相变热力学及相变动力学过程,最后采用液固两层构型法,描述了Ｃｕ晶体的生长过程。     

Molecular interactions and crystal packing in nematogen: Computational thermodynamic approach

A computational thermodynamic approach of molecular interactions in a nematogen p-n-alkyl benzoic acid (nBAC) molecule with an alkyl group butyl (4BAC) has been carried out with respect to translational and orientational motion. The atomic net charge and dipole moment at each atomic center were evaluated using the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrödinger perturbation theory along with multicentered-multipole expansion method were employed to evaluate long-range intermolecular interactions, while a 6-exp potential function was assumed for short-range interactions. Various possible geometrical arrangements of molecular pairs with regard to different energy components were considered, and the energetically favorable configuration was found to understand the crystal packing picture. Furthermore, these interaction energy values are taken as input to calculate the configurational entropy at room temperature (300 K), nematic-isotropic transition temperature (386 K) and above transition temperature (450 K) during different modes of interactions. An attempt has been made to describe interactions in a nematogen at molecular level, through which one can simplify the system to make the model computationally feasible in understanding the delicate interplay between energy and entropy, that accounts for mesomorphism and there by to analyze the molecular structure of a nematogen.     

Ordering in higher homologous series of <Emphasis Type="Italic">p-n</Emphasis>-alkylbenzoic acids having eight alkyl chain carbon atoms: a computational analysis

A computational analysis of ordering in the higher homologous series of p-n-alkylbenzoic acids (nBAC) having 8(8BAC) carbon atoms in the alkyl chain was performed based on quantum mechanics and intermolecular forces. The atomic charge and dipole moment at each atomic centre were evaluated using the all-valence electron CNDO/2 method. The modified Rayleigh-Schrödinger perturbation theory and the multi-center-multipole expansion method were employed to evaluate long-range intermolecular interactions, while a 6-exp potential function was assumed for short-range interactions. The total interaction energy values obtained in these computations were used as input for calculating the probability of each configuration in a noninteracting and nonmesogenic solvent (i.e., benzene) at room temperature (300 K) using the Maxwell-Boltzmann formula. The molecular parameters of 8BAC, including the total energy, binding energy, and total dipole moment, were compared with those of 7BAC and 9BAC. The present article offers a theoretical support for the experimental findings.     

A computational analysis of ordering in 2O.4 based on quantum mechanics and intermolecular forces

A computational analysis of ordering in p-ethoxybenzylidene-p-n-butylaniline (2O.4) has been carried out based on quantum mechanics and intermolecular forces. The evaluation of atomic charges and dipole moments at each atomic center has been carried out using the CNDO/2 method. The configuration energy has been computed using the modified Rayleigh-Schrödinger perturbation method at an interval of 1 Å in translation and 10° in rotations. The various possible geometrical arrangements of molecular pairs during the different modes of interactions have been considered, and the most favorable configuration of pairing has been obtained. A comparative picture of the molecular parameters, such as the total energy, binding energy, and total dipole moment of 2O.4 with other nematogen 4-4′-di-n-propoxy-azoxybenzene (DPAB) and 5-(trans-4-ethylcyclohexyl)-2-(4-cyanophenyl)-pyrimidine (ECCPP), has been given. The results are discussed in the light of experimental and other theoretical observations.     

Configurational specificity of stacking interactions in DNA base pairs: A computational analysis

A theoretical study of stacking patterns of various hydrogen-bonded base pair complexes has been undertaken. Modified Rayleigh-Schrodinger perturbation theory for intermediate range interactions, has been employed to evaluate the stacking interactions using multicentered-multipole expansion method. Net atomic charge and corresponding dipole components located at each of the atomic centers have been computed by CNDO/2 method. An analysis of the intermolecular forces involved in the stable formation of the various base pair complexes, has been presented and the results have been discussed in the light of experimental as well as other theoretical observations. The possibility of relative preference of the left-handed configuration for alternating sequences has been quantitatively explored.     

Influence of the Excited States of Atomic Nitrogen N(<Superscript>2</Superscript>D) and N(<Superscript>2</Superscript>P) on the Transport Properties of Nitrogen. Part I: Atomic Nitrogen Properties

In this paper, calculated values of the viscosity and thermal conductivity of atomic nitrogen, taking into account three species (the ground and two excited states), are presented. The calculations, which assume that the temperature dependent probability of occupation of the states is given by the Boltzmann factor, are performed for atmospheric-pressure in the temperature range from 1,000 to 20,000 K. Six collision integrals are used in calculating the transport coefficients and we have introduced new averaged collision integrals where the weight associated at each interacting species pair is the probable collision frequency. The influence of the collision integral values and energy transfer between two different species is studied. These results are compared which those of published theoretical studies.     

Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods

Recently developed correlation consistent basis sets for the first row transition metal elements Sc-Zn have been utilized to determine complete basis set (CBS) scalar relativistic electron affinities, ionization potentials, and 4s(2)3d(n-2)-4s(1)d(n-1) electronic excitation energies with single reference coupled cluster methods [CCSD(T), CCSDT, and CCSDTQ] and multireference configuration interaction with three reference spaces: 3d4s, 3d4s4p, and 3d4s4p3d'. The theoretical values calculated with the highest order coupled cluster techniques at the CBS limit, including extrapolations to full configuration interaction, are well within 1 kcal/mol of the corresponding experimental data. For the early transition metal elements (Sc-Mn) the internally contracted multireference averaged coupled pair functional method yielded excellent agreement with experiment; however, the atomic properties for the late transition metals (Mn-Zn) proved to be much more difficult to describe with this level of theory, even with the largest reference function of the present work.     

Visualization of electron correlation in autoionizing states above the 3p threshold in magnesium

The conditional probability density has been calculated for a number of autoionizing states (AIS) in Mg above the 3p threshold. The correlation in such high energy AIS has not been extensively studied and provides insight into the rovibrator behavior of two-electron atoms. The calculations have been done by configuration interaction (CI) with a B-spline basis. This allows for the simultaneous study of the effects of electron correlation and the widths and angular distribution of photoelectrons in multiphoton ionization. The states have been assigned approximate vibrational quantum numbers, and a correlation between the approximate quantum numbers and the photoelectron distribution is observed. Probability distribution for one electron when the other, represented by the small spike, is at its most probable distance from the nucleus. This is a distribution for the doubly-excited 1S(e) state commonly labeled as the 4s2 state.     

Pair correlation functions and a free energy functional for the nematic phase

In this paper we have presented the calculation of pair correlation functions in a nematic phase for a model of spherical particles with the long-range anisotropic interaction from the mean spherical approximation (MSA) and the Percus-Yevick (PY) integral equation theories. The results found from the MSA theory have been compared with those found analytically by Holovko and Sokolovska [J. Mol. Liq. 82, 161 (1999)]. A free energy functional which involves both the symmetry conserving and symmetry broken parts of the direct pair correlation function has been used to study the properties of the nematic phase. We have also examined the possibility of constructing a free energy functional with the direct pair correlation function which includes only the principal order parameter of the ordered phase and found that the resulting functional gives results that are in good agreement with the original functional. The isotropic-nematic transition has been located using the grand thermodynamic potential. The PY theory has been found to give a nematic phase with pair correlation function harmonic coefficients having all the desired features. In a nematic phase the harmonic coefficient of the total pair correlation function h(x1,x2) connected with the correlations of the director transverse fluctuations should develop a long-range tail. This feature has been found in both the MSA and PY theories.     

1-乙基-3-甲基咪唑四氟硼酸盐离子液体的量子化学研究

The results of the quantum chemistry study of the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM+BF4-) were reported. The ab initio method and density functional theory (B3LYP method) was used to optimize the stable structure of the gas phase ion pair at the level of 6-311++G** basis set, respectively. An IR spectra for EMIM+BF4- were obtained through the vibrational analysis. The changes of atomic charge assignments have been investigated using the Natural Bond Orbital method. The computational results show that there exist hydrogen bonds and other weak interactions between the cation and the anion. Using counterpoise correction method to estimate the basis set superposition error, the interaction energy between the cation and anion is 346.78 kJ/mol.     

Ordering in homologous series of 4′-<Emphasis Type="Italic">n</Emphasis>-alkyl-4-cyanobiphenyl (<Emphasis Type="Italic">n</Emphasis>CB)—A comparative computational study

A comparative computational analysis of molecular ordering in homologous series of monotropic nematic liquid crystal 4′-n-alkyl-4-cyanobiphenyl (nCB) molecules with alkyl groups, butyl (4CB), pentyl (5CB), hexyl (6CB), heptyl (7CB), has been carried out with respect to translational and orientational motion. The atomic net charge and dipole moment at each atomic center were evaluated using the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory and the multicenter-multipole expansion method were employed to evaluate long-range intermolecular interactions, while a 6-exp potential function was assumed for short-range interactions. Various possible geometrical arrangements of molecular pairs with regard to different energy components were considered, and the most favorable configuration was found. A comparative picture of molecular parameters, such as total energy, binding energy, and total dipole moment of 4CB, 5CB, 6CB, and 7CB, is given. The results are discussed in the light of other theoretical observations.     

Double-proton transfer in adenine-thymine and guanine-cytosine base pairs. A post-Hartree-Fock ab initio study

The results of a comprehensive study on the double-proton transfer in Adenine-Thymine (AT) and Guanine-Cytosine (GC) base pairs at room temperature in gas phase and with the inclusion of environmental effects are obtained. The double-proton-transfer process has been investigated in the AT and GC base pairs at the B3LYP/6-31G(d) and MP2/6-31G(d) levels of theory. It has been predicted that the hydrogen-bonded bases possess nonplanar geometries due to sp3 hybridization of nitrogen atoms and because of the soft intermolecular vibrations in the molecular complexes. An analysis of the energetic parameters of the local minima suggests that rare AT base pair conformation is not populated due to the shallowness of this minimum, which completely disappears from the Gibbs free energy surface. The stabilization of canonic or rare forms of the DNA bases by water molecules and metal cations has been predicted by calculating the optimal configuration of charges (using differential product/transition state stabilization approach) followed by calculations of the interactions between the base pair and a water/sodium cation.     

Local atomic structures of palladium nanowire

In this paper, investigation of the structure of palladium nanowire has been performed by using genetic algorithm simulation based on the molecular dynamics. Our calculation employs a well-fitted, tight-binding many-body potential for Pd atoms. Some local atomic structures and defects in nanowires have been reported. The melting behavior of palladium nanowire has also been investigated. An interesting result is that the diffusion of the central atoms results in the beginning of the melting. The moving central atoms build up a monostrand atomic chain during the melting process. The single atomic chain is very stable which can exist in a wide temperature region (800-950 K). The formation of the single atomic chain causes some new defects in the nanowire. And the new defects result in the decrease of the thermal stability of the nanowire. Interestingly, the liquid from the nanowire melting has a supercooled feature because the splitting of the second peak of pair correlation function is observed. The curves of the internal energy and the local cluster are used to monitor the phase transition. The melting of the nanowire is not only due to the single atomic diffusion, but also the diffusion of the local clusters.     

Electron localizability indicators ELI and ELIA: the case of highly correlated wavefunctions for the argon atom

Electron localizability indicators based on the same-spin electron pair density and the opposite-spin electron pair density are studied for correlated wavefunctions of the argon atom. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations aiming at the understanding of the effect of local electron correlation when approaching the exact wavefunction. The populations of the three atomic shells of Ar atom in real space are calculated for each case.