Solid State and Structural Chemistry Unit

1. Anomalous Diffusion of molecules / ions in confined system
2. Breakdown of Stokes-Einstein Relationships
3. Separation of Atomic / Molecular mixtures with high separation Factor
4. Influence of inter-crystalline space on diffusion in zeolites

Welcome to the Computational Physical Chemistry Research Lab led by Prof. Subramanian Yashonath. The research in our group focusses on a few fundamental aspects. These are: (i) diffusion (ii) intermolecular interactions and (iii) phase transitions (iv) computational methods development. To study these, Molecular Dynamics and Monte Carlo simulations has been used extensively in our lab. Molecular Dynamics simulation is study of the dynamics of molecules by solving Hamiltonian’s equation of motion and Monte-Carlo is a computer simulation technique that uses stochastic random walk to evolve the system based on the Boltzmann factor.

Diffusion has been investigated in different condensed matter phases. In porous solids, way back, a surprising behaviour was seen : the diffusivity of a larger guest molecule is higher than that of the smaller guest molecule. This led to the Levitation Effect [Yashonath and Santikary, JPC (1994)]. We found that this behaviour is also seen in liquids (leading to breakdown of Stokes-Einstein relation for interacting systems). It is also seen for diffusion of ions in ionic solids. Without the intermolecular interactions, it is not possible to compute the properties of materials in a classical molecular dynamics and Monte Carlo simulation. Earlier, from this group several intermolecular potential functions have been proposed for a variety of systems: (i) methane in faujasite (ii) nasicons (iii) alkenes in zeolites (iv) aluminated faujasite, etc. In the area of phase transitions, simulations of several small molecular solids and unsaturated aromatic hydrocarbon solids have been investigated. Crystal to plastic crystal and order-disorder transitions in many different solids have been simulated. These include CCl4, CF4, biphenyl, p-terphenyl, terphenyl, stilbene, etc [Rao and Yashonath, JSSC, (1987)]. Existing computational methods for simulating phase transitions such as Parrinello-Rahman variable shape simulation cell method were modified from their original form to prevent rotation of the simulation cell [ Yashonath and Rao, Chem. Phys. Lett. (1985)]. Also, in recent times, method for the simulation of inhomogeneous systems using non-equilibrium Monte Carlo approach has been proposed.

Apart from these aspects in fundamental or basic science, we have tried to propose novel methods for separation of molecular mixtures. We have judiciously combined levitation effect and blow-torch effect to separate the components of the mixtures in opposite direction. This method is characterized by high efficiency, high separation factor as compared to existing separation methods and useful to separate atomic/molecular/ionic mixtures [Anil et. Al, JPCB, (2006)]. We have also studied the separation of hexane isomers in zeolite. The behaviour of dibranched hexane isomers in zeolite as well as separation of such branched hexane isomers from their linear counterpart, n-hexane (nC6), using zeolites is of great interest due to high research octane number (RON) of the branched isomers [Angela and Yashonath, JPCC, (2017)].