Browsing by Author "Shikha Dwivedi"

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Density functional theory of freezing of a system of conjugated oligomers parameterised via Gay–Berne potential
(Taylor and Francis Ltd., 2016) Shikha Dwivedi; Pankaj Mishra; Jokhan Ram
Density functional theory (DFT) of freezing is used to study the isotropic–nematic, isotropic–smectic A and nematic–smectic A phase transitions in a system of large, semi-flexible conjugated oligomers parameterised within Gay–Berne (GB) potential. The pair correlation functions of the isotropic fluid, used as structural inputs in the DFT, are calculated by solving the Percus–Yevick integral equation theory. Large number of spherical harmonic coefficients of each orientation-dependent functions has been considered to ensure the numerical accuracy at different densities and temperatures for the system of these model GB ellipsoids having large aspect ratio (length-to-breadth ratio). We found that the system of GB ellipsoids parameterised for conjugated oligomers shows stable isotropic, nematic and smectic A phases. At low temperatures, on increasing the density, isotropic fluid makes a direct transition to smectic A phase. Nematic phase get stabilised in between the isotropic and smectic A phases on increasing the temperature. Using the transition parameter obtained through the DFT, we have plotted the temperature–density and pressure–temperature phase diagrams which are found to be qualitatively similar to the one obtained in simulations for the systems with low aspect ratio GB particles. © 2016 Taylor & Francis.
Tunable attractive interaction and the phase diagram of a system of Gay-Berne ellipsoids: A density functional approach
(Elsevier B.V., 2016) Shikha Dwivedi; Pankaj Mishra; Ram Chandra Singh; Jokhan Ram
Density functional theory has been used to investigate the effect of the variation of attractive interaction on phase diagram of a system of axially symmetric liquid crystalline molecules interacting via Gay-Berne intermolecular potential. The pair correlation functions of the isotropic fluid, used as structural input in the density functional theory have been calculated by using Percus-Yevick integral equation theory. Considering the isotropic, nematic and smectic A phases as the candidate structures, we observe that the transition parameters and the topology of the phase diagram changes significantly with the variation in the strength of attractive interaction between the molecules. The dominance of the attractive interaction over repulsive one, is found to cause an enhanced tendency of the system to freeze into smectic A phase. Both isotropic-nematic and nematic-smectic A transition densities and pressure are found to decrease as we increase the strength of the attraction among the particles. The pair correlation functions and phase transition parameters are compared with the available computer simulation results of the similar model potential and are found to be in good qualitative agreement. © 2016 Elsevier B.V.