Articles written in Journal of Chemical Sciences
Volume 113 Issue 5-6 October 2001 pp 559-577
Diffusion of monatomic guest species within confined media has been understood to a good degree due to investigations carried out during the past decade and a half. Most guest species that are of industrial relevance are actually polyatomics such as, for example, hydrocarbons in zeolites. We attempt to investigate the influence of non-spherical nature of guest species on diffusion. Recent molecular dynamics (MD) simulations of motion of methane in NaCaA and NaY, benzene in NaY and one-dimensional channels AlPO4−5, VPI−5 and carbon nanotube indicate interesting insights into the influence of the host on rotational degrees of freedom and orientational properties. It is shown that benzene in one-dimensional channels where the levitation parameter is near unity exhibits translational motion opposite to what is expected on the basis of molecular anisotropy. Rotational motion of benzene also possesses rotational diffusivities around
Volume 115 Issue 5-6 October 2003 pp 543-552
In zeolites, diffusion is often accompanied by a reaction or sorption which in turn can induce temperature inhomogeneities. Monte Carlo simulations of Lennard-Jones atoms in zeolite NaCaA are reported for the presence of a hot zone presumed to be created by a reaction or chemi- or physi-sorption site. These simulations show that the presence of localized hot regions can alter both kinetic and transport properties such as diffusion. Further, we show that enhancement of diffusion constant is greater for systems with larger barrier height, a surprising result that may be of considerable significance in many chemical and biological processes. We find an unanticipated coupling between reaction and diffusion due to the presence of a hot zone in addition to that which normally exists via concentration. Implications of this coupling for the product profile of a reaction are discussed. We also propose a mechanism by which mobility of ions or diffusion of molecular species within biomembranes may take place.
Volume 118 Issue 1 January 2006 pp 135-154
Solid state ionic conductors are important from an industrial viewpoint. A variety of such conductors have been found. In order to understand the reasons for high ionic conductivity in these solids, there have been a number of experimental, theoretical and computational studies in the literature. We provide here a survey of these investigations with focus on what is known and elaborate on issues that still remain unresolved. Conductivity depends on a number of factors such as presence of interstitial sites, ion size, temperature, crystal structure etc. We discuss the recent results from atomistic computer simulations on the dependence of conductivity in NASICONs as a function of composition, temperature, phase change and cation among others. A new potential for modelling of NASICON structure that has been proposed is also discussed.
Volume 121 Issue 5 September 2009 pp 921-927
Molecular dynamics simulations are reported on the structure and dynamics of 𝑛-decane and 3-methylpentane in zeolite NaY. We have calculated several properties such as the center of mass-center of mass rdf, the end-end distance distribution, bond angle distribution and dihedral angle distribution. We have also analysed trajectory to obtain diffusivity and velocity autocorrelation function (VACF). Surprisingly, the diffusivity of 3-methylpentane which is having larger cross-section perpendicular to the long molecular axis is higher than 𝑛-decane at 300 K. Activation energies have been obtained from simulations performed at 200 K, 300 K, 350 K, 400 K and 450 K in the NVE ensemble. These results can be understood in terms of the previously known levitation effect. Arrhenious plot has higher value of slope for 𝑛-decane (5.9 kJ/mol) than 3-methylpentane (3.7 kJ/mol) in agreement with the prediction of levitation effect.
Volume 124 Issue 1 January 2012 pp 159-166
A molecular dynamics study of the dependence of diffusivity of the cation on ionic radii in molten AgI is reported.We have employed modified Parinello-Rahman-Vashistha interionic pair potential proposed by Shimojo and Kobayashi. Our results suggest that the diffusivity of the cation exhibits an increase followed by a decrease as the ionic radius is increased. Several structural and dynamical properties are reported.
Volume 135, 2023
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