122 research outputs found
Electric fields with ultrasoft pseudo-potentials: applications to benzene and anthracene
We present density functional perturbation theory for electric field
perturbations and ultra-soft pseudopotentials. Applications to benzene and
anthracene molecules and surfaces are reported as examples. We point out
several issues concerning the evaluation of the polarizability of molecules and
slabs with periodic boundary conditions.Comment: 10 pages, 7 figures, to appear in J. Chem. Phy
Biaxial order parameter in the homologous series of orthogonal bent-core smectic liquid crystals
The fundamental parameter of the uniaxial liquid crystalline state that governs nearly all of its physical properties is the primary orientational order parameter (S) for the long axes of molecules with respect to the director. The biaxial liquid crystals (LCs) possess biaxial order parameters depending on the phase symmetry of the system. In this paper we show that in the first approximation a biaxial orthogonal smectic phase can be described by two primary order parameters: S for the long axes and C for the ordering of the short axes of molecules. The temperature dependencies of S and C are obtained by the Haller's extrapolation technique through measurements of the optical birefringence and biaxiality on a nontilted polar antiferroelectric (Sm-APA) phase of a homologous series of LCs built from the bent-core achiral molecules. For such a biaxial smectic phase both S and C, particularly the temperature dependency of the latter, are being experimentally determined. Results show that S in the orthogonal smectic phase composed of bent cores is higher than in Sm-A calamatic LCs and C is also significantly large
Influence of a Mechanical Field on the Liquid Crystalline to Isotropic Phase Transformation
Electrically tunable refractive index in the dark conglomerate phase of a bent-core liquid crystal
Here we report an electrically tunable refractive index observed in an isotropic liquid crystal phase known as the dark conglomerate (DC) phase. This unusual change in the refractive index which has not been reported before in the DC phase of other bent-core liquid crystals occurs because of a series of electric-field-driven transformations that take place in the DC phase of the studied bent-core liquid crystal. These transformations give rise to a decrease in the refractive index of the system, when an electric field is applied across the device, and no change in the birefringence is seen during such behavior. The electro-optic phenomenon is described in detail and the possibility of exploiting this for a number of liquid crystal based device applications is discussed
Mesure de l'Anisotropie des Indices de Réfraction des Cristaux Liquides: Interpretation des Différences Observées lors de I'Utilisation des Diverses Méthodes
Structural Defects and Phase Transition in a Lyotropic System: Optical Birefringence and Order Parameter Measurements
Relation between Wavelength Dispersion of Refractive Index and Birefringence of Polymers Estimated by Quantum Chemical Calculation and Chemical Structure
- …