Molecular ordering of 4O.2 compound in a dielectric medium at room temperature‐A theoretical approach

The molecular ordering of N‐(4‐n‐butoxybenzylidene)‐4′‐ethyaniline [4O.2] in a dielectric medium (benzene) has been carried out on the basis of statistical mechanics and intermolecular forces. The atomic net charge and atomic dipole moment at each atomic centre has been evaluated using the CNDO/2 method. The modified Rayleigh‐Schrodinger perturbation theory with multicentered‐multipole expansion method has been employed to evaluate the long‐range intermolecular interactions, while ‘6‐exp’ potential function has been assumed for the short‐range interactions. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium at room temperature (300K) using the MB‐formula. The flexibility of various interacting configuration has been studied in terms of variation of probability due to departure from the most probable configuration. A comparative picture of the molecular parameters like total energy, binding energy and total dipole moment has been given. An attempt has been made to analyse the characteristic features of nematogenic 4O.2 compound in terms of its relative order. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The role of a dielectric medium in a smectogenic Schiff base compound: A computational analysis

A computational analysis of ordering in a smectogenic Schiff base compound, N-(4-n-heptyloxybenzylidine)-4-hexylaniline, has been carried out with the help of quantum mechanics and computer simulation. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic-charge and atomic dipole moment at each atomic center. The modified Rayleigh-Schrödinger perturbation theory with the 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 interaction-energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium at the phase-transition temperature (353 K). An attempt has been made to develop a new model of a smectogen in a dielectric medium. The present investigation provides theoretical support to the experimental observations.     

7-Hexyloxy-3-[4’-(3-methylbutyloxy) phenyl]-4H-1-benzopyran-4-one: Study of Smectic behaviour and UV absorption profile

The intermolecular interaction energies between a pair of 7-Hexyloxy-3-[4’-(3-methylbutyloxy) phenyl]-4H-1-benzopyran-4-one (HMBPB) molecules have been estimated with respect to translational and orientational motions. The complete neglect differential overlap (CNDO/S) method has been employed to calculate the net atomic charge and atomic dipole moment components at each atomic center. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the 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 to calculate the probability of each configuration at room temperature (300K), and isotropic-smectic transition temperature (412.6K). Molecular arrangements inside a bulk of materials and smectic behavior of the compound in terms of their relative order have been discussed. Translational and rotational rigidity of the molecule has been analyzed to understand the smectic behaviour. The UV absorption profile has been estimated using CNDO/S, and INDO/S methods.     

Role of dielectric medium on benzylidene aniline: A computational analysis

A computational analysis of ordering in N-(p-n-ethoxy benzylidene)-p-n-butyl aniline (2O.4) was performed based on quantum mechanics and intermolecular forces. The atomic charge and dipole moment at atomic centre were evaluated using the all valance electron CNDO/2 method. The modified Rayleigh-Schrodinger perturbation theory and multicentre—multipole expansion method were employed to evaluate long-range intermolecular interaction, 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 parameter of 2O.4, including the total energy, binding energy, and total dipole moment were compared with N (p-n-butoxy benzylidene)-p-n-ethyl aniline (4O.2). The present article offer theoretical support to the experimental “observations, as well as a new and interesting way of looking at liquid crystalline molecule in a dielectric medium.     

Role of dielectric medium on mesogenic compounds (BCHs) at phase transition temperature: A comparative computational analysis

A comparative computational analysis on two liquid crystalline disubstituted biphenylcyclohexanes (BCHs) of general formula R‐C₆H₁₀‐C₆H₄‐X with R: C₃H₇; X: H (BCH30) and R: C₅H₁₁; X: CN (BCH5CN) has been carried out on the basis of quantum mechanics and intermolecular forces. The evaluation of atomic charge and dipole moment at each atomic centre has been carried out through an all‐valence electron (CNDO/2) method. The configurational energy has been computed using the Rayleigh‐Schrodinger perturbation method. The total interaction energy values obtained were used to calculate the probability of each configuration in dielectric medium (i.e. non‐interacting and non‐mesogenic solvent, benzene) at room temperature, transition temperature and above transition temperature using the Maxwell‐Boltzmann's formula. The flexibility of various interacting configurations has been studied in terms of variation of probability due to small departures from the most probable configurations. Further, the various possible geometrical arrangements between a molecular pair during the different modes of interactions have been considered. An attempt has been made to develop a new and interesting model for mesogenic compounds in a dielectric medium. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Computational analysis of ordering in higher homologous series of nBAC: The effect of a dielectric medium

A computational analysis of ordering in higher homologous series of p-n-alkylbenzoic acids (nBAC) that have 7 (7BAC) and 9 (9BAC) carbon atoms in the alkyl chain has been carried out on the basis of quantum mechanics and intermolecular forces. The molecular geometry of 7BAC and 9BAC has been constructed on the basis of published crystallographic data with the standard values of bond lengths and bond angles. The evaluation of atomic charge and dipole moment at each atomic center has been carried out through the complete neglect differential overlap (CNDO/2) method. The configurational energy has been computed via the Rayleigh-Schrödinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium at the nematic-isotropic-transition temperature through the use of the Maxwell-Boltzmann formula. It has been observed that there is a considerable rise in the probability of interactions, although the order of preference remains the same. The present article offers theoretical support to the experimental observations. In addition, this provides a new way of looking at the liquid-crystalline molecules in a dielectric medium.     

Statistical Study of Molecular Ordering in a Nematogenic Compound – A Computational Analysis

A computational Analysis has been carried out to determine the configurational preference of a pair of a nematogen, 4,4′‐azodiphenetole (C₂H₅‐O‐C₆H₄‐N=N‐C₆H₄‐O‐C₂H₅) [AZO] molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to compute the atomic charge and atomic dipole at each atomic centre. Configurational energy has been computed using modified Rayleigh‐Schrodinger perturbation method. The interaction energy values obtained through these computations were used to calculate the probability of each configuration at phase transition temperature using Maxwell‐Boltzmann formula. Further, the flexibility of various configurations has been studied in terms of variation of probability due to small departures from the most probable configuration. Molecular parameters like total energy, binding energy and total dipole moment have been given. Results have been discussed in the light of experimental as well as other theoretical observations.     

Computational analysis of ordering in non-liquid crystalline versus liquid crystalline materials with special reference to <Emphasis Type="Italic">n</Emphasis>BAC

A computational analysis of ordering in non-liquid crystalline p-n-alkyl benzoic acid, having 1 (1BAC), 2 (2BAC) and 3(3BAC) carbon atoms in the alkyl chain has been carried out with respect to translatory and orientational motions, but detailed results are reported only for 3BAC. The evaluation of net atomic charges and dipole moments at each atomic center has been carried out using complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory along with the multicentered-multipole expansion method has been employed to evaluate long-range interactions, while a “6-exp” potential function has been assumed for short-range interactions. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible arrangements of a molecular pair have been considered. A comparative picture of molecular parameters, such as total energy, binding energy, and total dipole moment of 3BAC with higher homologous series liquid crystalline compounds having 4(4BAC), 5(5BAC), and 6(6BAC) alkyl chain carbon atoms, has been given. It is found that, if a suitable functional group is attached to 3BAC, so that the length to breadth ratio is increased, the molecule will show a change in the long-range order, the phase transition temperature and other liquid crystalline properties.     

Probabilistic and thermodynamic approach on phase behavior of nematic liquid crystals: A comparative study

The systems chosen for the present investigation, p-n-alkylbenzoic acid (nBAC; n = 6, 7) exhibits nematic-isotropic transition. A comparative study based on quantum probabilistic 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 centre 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, while the ‘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 probability of occurrence of a particular configuration using the Maxwell-Boltzmann formula. Further, thermodynamic parameters such as Helmholtz free energy, and entropy at room temperature (300 K), and nematic-isotropic transition temperatures have been computed. An attempt has been made to understand the structure-phase behaviour relationship at molecular level.     

Theoretical study of closo-decaborate novel nematogen: Thermodynamic behavior and phase stability

The present article deals with the thermodynamic behavior and phase stability of closo-decaborate nematogen viz. dinitrogen-10-(4-pentyl-1-thiacyclohexyl)-closo-decaborate (DPTD) at a molecular level. The atomic net charge and dipole moment at each atomic center have been evaluated using the complete neglect differential overlap (CNDO) method. The modified Rayleigh–Schrodinger perturbation method along with multicentered–multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for the short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature (300 K), nematic–isotropic transition temperature (435 K), and above transition temperature (500 K) using the Maxwell–Boltazman formula. Further, the entropy of each configuration has been computed during the different modes of interactions. The adopted framework provides valuable information on thermodynamic behavior, and phase stability of novel nematogen based on parameters, i.e., molecular and thermodynamic, introduced in this article.     

Conformational Behavior and Influence of Organic Solvents on a Strong Polar Group Nematogen at Room Temperature—A Computational Model

The conformational behavior and influence of organic solvents on a nematogen, 4’-n-alkyl-4-cyanobiphenyl, with strong polar group propyl (3CB) that is of commercial and application interest has been studied with respect to the 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 with the multicentered-multipole expansion method has been employed to evaluate the long-range interactions, and a “6-exp.” potential function has been assumed for the short-range interactions. The minimum energy configurations obtained during the different modes of interactions have been taken as input to calculate the configurational probability using the Maxwell–Boltzmann formula in nonpolar organic solvents, i.e., carbon tetrachloride (CCl₄), and chloroform (CHCl₃) at room temperature 300 K. It has been observed that the molecules show the interesting property in the organic solvents. The interaction energies of dimer complexes have been taken into consideration in order to investigate the most energetically stable configuration. An attempt has been made to develop an interesting computational model for nematogen at molecular level.     

Order–Disorder Phenomenon of Nematogens at Molecular Level—A Computational Approach

The phase behavior of nematogenic p-n-Alkoxy cinamic acids (nOCAC) with alkyl chain carbon atoms (n = 2,4) has been reported with respect to the 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 with the multicentered-multipole expansion method has been employed to evaluate the long-range interactions, and a “6-exp.” potential function has been assumed for the short-range interactions. The minimum energy configurations obtained during the different modes of interactions have been taken as input to calculate the configurational probability using the Maxwell–Boltzmann formula in nonpolar organic solvents, i.e., carbon tetrachloride (CCl₄), and chloroform (CHCl₃) at room temperature 300 K. Further, entropy of each configuration has been computed. It has been observed that the molecules show the remarkable behavior in the solvents. An attempt has been made to develop new and interesting computational model for nematogens in the solvents and order–disorder phenomenon at molecular level.     

A Comparison of Pair Potential for Some Polar and Non-Polar Mesogenic Molecules

Asymmetry of pair potential plays a crucial role in the formation of mesophases in molecular systems. Variation of such asymmetry is closely related to the constituents of the molecules as well as their positions. To investigate the asymmetry as well as its effect on molecular behavior, a few polar biphenyl and non-polar 2,5 disubstituted pyridine derivatives have been chosen. The intermolecular interaction energy between a pair of molecules has been calculated with the help of a standard method as prescribed by Claverie (Claverie, P. (1978). Elaborations of approximate formulas for interactions between large molecules: Applications in organic chemistry. In: B. Pullman (Eds.), Inter Molecular Interactions from Diatomic to Biopolymers, J. Wiley & Sons Ltd.: Hoboken, NJ, 217–226.). Molecular geometry of all the selected systems was fully optimized without any constraint, and the net atomic charge and the dipole moment on each atomic center was calculated using the Gaussian03 program with density functional B3LYP method using 6-31G** as the basis set. The dispersion and the short range repulsion energy terms have been calculated using semiempirical Kitaigorodskii's “6-exp” formula. An attempt has been made to explain the phase sequences on the basis of the ratios of various interaction energy terms.

Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.     

Refractive index dispersion of spinel Zn2TiO4 single crystal

The transmittance and absorption spectra of a high‐quality Zn₂TiO₄ single crystal have been measured along the a‐axes at room‐temperature in the range of 200‐1000 nm. The wavelength dependent refractive index, extinction coefficient, real and imaginary parts of the complex dielectric constant of the Zn₂TiO₄ crystal have been derived from the measured T and α spectra. By fitting the refractive index spectrum, the Sellmeier dispersion equation of the Zn₂TiO₄ crystal has been obtained. The validity of Cauchy‐Sellmeier equation has been evaluated in the energy range of 2.90–3.20 eV representing the Urbach tail. Applying the single‐effective oscillator model, the dispersion energy E_d and the oscillator energy E₀ have been determined as 18.76 and 5.05 eV, respectively. The obtained dispersion energy E_d takes on ionic crystal value. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase stability and ordering of nematogen at molecular level: A computer-aided modeling

The present article deals with the phase stability and ordering of nematogen, viz., 6-octyloxy-2-naphthylyl-4-octoxybenzoate (ONOB) at molecular level. A comparative picture has been given between molecular charge distribution, and phase stability based on AM1, PM3, CNDO, and MNDO methods. The modified Rayleigh–Schrodinger perturbation method along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a “6-exp” potential function has been assumed for the short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature, nematic-isotropic transition temperature, and above transition temperature using the Maxwell–Boltzmann formula. Further, the entropy of each configuration has been computed during the different modes of interactions. An effort has been made to develop a computational model at molecular level based on configurational entropy, and translational rigidity parameters introduced in this article.     

Experimental observations of the thermal stability of high-k gate dielectric materials on silicon

High-k dielectric materials including zirconium oxide and hafnium oxide produced by atomic layer deposition have been evaluated for thermal stability. As-deposited samples have been compared with rapid thermal annealed samples over a range of source/drain dopant activation temperatures consistent with conventional complimentary metal oxide semiconductor polysilicon gate processes. Results of this initial investigation are presented utilizing analyses derived from X-ray diffraction (XRD), X-ray reflectometry (XRR), medium energy ion spectroscopy, high resolution transmission electron microscopy (HRTEM), tunneling atomic force microscopy, scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectroscopy. Changes in interface and surface roughness, percent crystallinity and phase identification for each material as a function of anneal temperature have been determined by XRD, XRR and HRTEM. Finally, high-k wet etch issues are presented relative to subsequent titanium silicide blanket film resistivity values.     

Dielectric studies of lead nitrate phosphate single crystals

Ferroelectric Lead Nitrogen Phosphate (LNP) single crystals have been synthesized using the controlled reaction between lead nitrate and orthophosphoric acid solutions by slow diffusion process in silicagel medium. The colourless transparent LNP crystals upto 6 × 4 × 3 mm³ in size have been grown at room temperature. The dielectric measurements have been carried out in the temperature range between 300 to 690 K. The effect of applied frequency on the dielectric constants and dielectric losses has been investigated. It has been observed that the mechanism of the dielectric behaviour is different in the lower and higher frequency and temperature ranges. The activation energy of the oscillators has been calculated and found to be 1.125 eV. Attempt has been made to draw some qualitative conclusions, taking in view, the existing theories of various kinds of polarizations and implications.     

Dielectric properties of ferroelectric lead hydrogen phosphate single crystals

The ferroelectric lead hydrogen phosphate (LHP) single crystals have been grown by employing the gel technique. The controlled reaction between lead nitrate and orthophosphoric acid solutions by diffusion process in gel medium has been used. The dielectric constant (ϵ′) and the dielectric loss (ϵ″) have been measured for the first time as a function of frequency in the range 10² to 10⁴ Hz. They have also been determined as a function of temperatures in the range 300 to 680 K. The polarisation effect contributing to the dielectric constant has been studied. It has been observed that the mechanism of the dielectric behaviour is different in the lower and higher temperatur and frequency ranges. The activation energy of the oscillators has been calculated and found to be 1.12 eV. Attempt has been made to draw some qualitative conclusions, taking in view, the existing theories of various kinds of polarization and implications have been discussed.     

Properties of GeSi Nanocrystals Embedded in Hexagonal SiC

In this paper high‐resolution electron microscopy investigations and molecular dynamics simulations of GeSi nanocrystals buried in 4H‐SiC are performed, showing that the experimentally observed shapes of the GeSi nanocrystals are strongly correlated with their orientational relationships. Measurements of the lattice spacing suggest that the nanocrystals are strained. Quantum confinement in selected nanocrystals has been detected using spatially‐resolved electron energy loss spectroscopy performed in conjunction with atomic resolution annular dark‐field scanning TEM.     

Molecular organization in liquid crystals: A comparative computational analysis

A comparative computational analysis of molecular organization in four-nematogenic acids (nOCAC) having two, four, six, and eight carbon atoms in the alkyl chain is carried out with respect to translatory and orientational motions. The evaluation of the atomic charge and dipole moment at each atomic center is performed through the complete neglect differential overlap (CNDO/2) method. The Rayleigh-Schrödinger perturbation theory, along with the multicentered-multipole expansion method, is employed to evaluate the long-range interactions, while the “6-exp” potential function is assumed for short-range interactions. The total interaction-energy values obtained through these computations are used to calculate the probability of each configuration at the phase transition temperature via the Maxwell-Boltzmann formula. Further, the flexibility of various configurations is studied in terms of variation of probability due to small departures from the most probable configuration. A comparative picture of molecular parameters, such as the total energy, binding energy, and total dipole moment, is given. An attempt is made to explain the nematogenic behavior of these liquid crystals in terms of their relative order and, thereby, to develop a molecular model for the liquid crystallinity.