Computer simulation of ordering in bipolar nematogen H6CBP at phase transition temperature

Praveen, P. Lakshmi; Ojha, Durga P.

doi:10.1016/j.matchemphys.2010.03.074

Cited by 16 publications

(6 citation statements)

References 16 publications

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“…Recently, we have reported [12,13] the physical behaviour of nematic liquid crystals in benzene (i.e. non-interacting, non-mesogenic and non-polar solvent) -as has Kundu et al [14].…”

Section: Introductionmentioning

confidence: 71%

Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

Praveen¹,

Ojha²

2011

Liquid Crystals

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To cite this article: P. Lakshmi Praveen & Durga P. Ojha (2011) Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent, Liquid Crystals, 38:8, 963-970, A semi-empirical analysis has been carried out on two nematic liquid crystals, 4-cyanophenyl-4 -n-pentylbenzoate (CPPB) and 4-cyanophenyl-4 -n-pentoxybenzoate (CPPOB), using the CNDO/S + CI and INDO/S + CI methods. These methods have been applied to simulate and analyse the electronic structures, spectra and ultraviolet (UV) stability of the systems. Phase stability of the systems has also been studied based on molecular charge distribution. The electronic transitions, absorption wavelength, HOMO and LUMO energies are calculated. Furthermore, UV stability of the molecules is discussed in the light of absorption wavelength and electronic transition oscillator strength (f ). The effect of solvent and substituent on these factors is discussed. A comparison among different solvents is also made. These absorption spectra will provide a valuable database for further computational analysis and the other experimental investigations. IntroductionLiquid crystals represent a class of complex fluids that has opened many doors for us to learn a great deal about molecular interactions [1], phase behaviour, transitions and the art of soft condensed matter. These molecular fluids show specific optical properties due to the anisotropy of molecular organisation [2]. This anisotropy plays an important role in applications of the electrical effect, display devices, spatial modulators, etc. The bulk order in these materials has profound control on the way light [3] and electricity behave in the material. A unique insight into this behaviour provides not only information about the particular material under consideration, but also about the global properties of anisotropic fluids and their relationships to other chemical structures and/or physical phenomena.Despite their various applications [4][5][6][7], liquid crystals (LCs) belonging to the 4-cyanophenyl-4 -n-alkylbenzoate (CPnB) homologous series and their composites are less studied than those from cyanobiphenyl series. The simulation of electronic spectra by computational chemistry tools is particularly appealing since a large number of methods have been elaborated and employed to calculate the molecular vertical excitation energies, absorption wavelength and oscillator strength of electronic transitions.In view of this, methods based on Time Dependent Density Functional Theory (TDDFT)

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“…Recently, we have reported [12,13] the physical behaviour of nematic liquid crystals in benzene (i.e. non-interacting, non-mesogenic and non-polar solvent) -as has Kundu et al [14].…”

Section: Introductionmentioning

confidence: 71%

Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

Praveen¹,

Ojha²

2011

Liquid Crystals

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“…In fact, the inclusion of higher order multipoles does not significantly affect the electrostatic interaction energy and the calculation only up to dipole-dipole term gives satisfactory result [10][11][12][13][14]20]. The computation of electrostatic term has, therefore, been restricted only up to dipole-dipole energy term.…”

Section: Computation Of Interaction Energy At Various Configurationsmentioning

confidence: 99%

“…The total interaction energy values obtained through these computations have been used as an input to calculate the probability of occurrence of a particular configuration i using the Maxwell-Boltzmann formula [20] in order to obtain a better insight:…”

Section: Computation Of Configurational Probabilitiesmentioning

confidence: 99%

Molecular Structure and Conformational Behavior of a Nematogen—A Statistical Approach

Praveen¹,

Ojha²

2011

Molecular Crystals and Liquid Crystals

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Molecular structure and conformational behavior of a nematogen p-ethoxy salicylidene-n-butyl aniline (ESBA) has been studied with respect to translational and orientational motions. The atomic net charge and dipole moment components at each atomic center have been evaluated using the complete neglect differential overlap (CNDO=2) method. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the longrange intermolecular interactions, and a 6-exp potential function has been assumed for short-range interactions. The interaction energy values obtained during the different modes of molecular interactions have been taken as input to calculate the configurational probability at room temperature (300 K). On the basis of stacking, in-plane, and terminal interaction energy calculations, all possible geometrical arrangements between the molecular pairs have been considered. The effect of nonmesogenic and noninteracting solvent (benzene) has also been studied. Further, the analysis of conformational behavior provides valuable information on configurational freedom of a molecule that may be useful in understanding the structure of phases and their transitions.

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“…The computer program INTER, originally developed by Claverie and later modified at Chemical Physics Group, Tata Institute of Fundamental Research, Bombay, India, by Govil and associates has been used for this purpose with further modification. According to the second-order perturbation theory for intermediate-range interactions [18], the total pair interaction energy of molecules (U pair ) is represented as the sum of various terms contributing to the total energy:…”

Section: Computation Of Interaction Energy At Various Configurationsmentioning

confidence: 99%

Molecular Order-Disorder Phenomenon of a Nematogen: A Computational Analysis

Praveen¹,

Ojha²

2010

Molecular Crystals and Liquid Crystals

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The system chosen for the present investigation, para-azoxyanisole (4AA), exhibits a nematic-isotropic transition temperature at 408 K. A computational analysis based on quantum mechanics and statistical thermodynamics has been carried out with respect to translational and orientational motions. The evaluation of net atomic charges and dipole moment at each atomic center has been carried out through the complete neglect differential overlap (CNDO=2) method. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, and the 6-exp potential function has been assumed for short-range interaction. The total interaction energy values obtained through these computations have been used as input to calculate the probability of occurrence of a particular configuration using the MaxwellBoltzmann formula. Further, thermodynamic parameters such as Helmholtz free energy, entropy at room temperature (300 K), nematic-isotropic transition temperature (408 K), and above transition temperature (500 K) have been computed. An attempt has been made to understand the order-disorder phenomenon exhibited by a nematogen and to develop a new and interesting model for structure-phase stability relationships at the molecular level.

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Computer simulation of ordering in bipolar nematogen H6CBP at phase transition temperature

Cited by 16 publications

References 16 publications

Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

Molecular Structure and Conformational Behavior of a Nematogen—A Statistical Approach

Molecular Order-Disorder Phenomenon of a Nematogen: A Computational Analysis

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