• Rajib Biswas

      Articles written in Journal of Chemical Sciences

    • Use of polydispersity index as control parameter to study melting/freezing of Lennard-Jones system: Comparison among predictions of bifurcation theory with Lindemann criterion, inherent structure analysis and Hansen-Verlet rule

      Sarmistha Sarkar Rajib Biswas Partha Pratim Ray Biman Bagchi

      More Details Abstract Fulltext PDF

      Using polydispersity index as an additional order parameter we investigate freezing/melting transition of Lennard-Jones polydisperse systems (with Gaussian polydispersity in size), especially to gain insight into the origin of the terminal polydispersity. The average inherent structure (IS) energy and root mean square displacement (RMSD) of the solid before melting both exhibit quite similar polydispersity dependence including a discontinuity at solid-liquid transition point. Lindemann ratio, obtained from RMSD, is found to be dependent on temperature. At a given number density, there exists a value of polydispersity index (𝛿P) above which no crystalline solid is stable. This transition value of polydispersity (termed as transition polydispersity, 𝛿P) is found to depend strongly on temperature, a feature missed in hard sphere model systems. Additionally, for a particular temperature when number density is increased, 𝛿P shifts to higher values. This temperature and number density dependent value of 𝛿P saturates surprisingly to a value which is found to be nearly the same for all temperatures, known as terminal polydispersity (𝛿TP). This value (𝛿TP ∼ 0.11) is in excellent agreement with the experimental value of 0.12, but differs from hard sphere transition where this limiting value is only 0.048. Terminal polydispersity (𝛿TP) thus has a quasiuniversal character. Interestingly, the bifurcation diagram obtained from non-linear integral equation theories of freezing seems to provide an explanation of the existence of unique terminal polydispersity in polydisperse systems. Global bond orientational order parameter is calculated to obtain further insights into mechanism for melting.

    • Role of solvation structure in the shuttling of the hydrated excess proton


      More Details Abstract Fulltext PDF

      The classic Marcus electron transfer reaction model demonstrated that a barrierless electron transfer reaction can occur when both the reactant and product have almost similar solvation environment. In our recently developed proton model, we have incorporated the pre-solvation concept and showed that it indeed facilitates the proton diffusion in aqueous solution. In this work, we further quantify the degree of pre-solvation using different structural parameters, e.g., tetrahedral order parameter, average numbers of hydrogen bonds. All theabove said parameters exhibit a very strong correlation with the proton share parameter. The more Zundel-like configurations have almost identical solvation environment for both the water molecules and support the presolvationconcept. However, in the case of Eigen-like configurations, the central hydronium and “special pair” water have distinctly different solvation structures.

    • Hydrophobic Hydration: A Theoretical Investigation of Structure and Dynamics


      More Details Abstract Fulltext PDF

      The presence of external solutes alters the local structures, and dynamics of water. The nature andextent of these structural modifications depend on several factors. Particularly, the chemical nature of the solute is very crucial. The alteration of water structure and dynamics in the presence of hydrophobic substances draws considerable attention in biological systems. The present work is focused on exploring the microscopic arrangement of solvation shells of tiny hydrophobic solute methane. We explore the tetrahedral order, local structural index, and van Hove self-correlation function to get a quantitative understanding. Weobserve a slight increase in the structural order of water molecules in methane’s first solvation shell, similar tothat of the low-temperature water. We also find that water facing the methane have lower structural order than bulk water. Furthermore, the water molecules in the first solvation shell around methane show relatively slower orientational relaxation.

      The hydrophobicity-induced alterations of water structural and dynamical properties are investigated using solvation shell decomposition. We observe the slower relaxation of selected water molecules staying longer time in methane first solvation shell. We find enhanced structural order in the methane first solvation shell and some dangling water molecules.

  • Journal of Chemical Sciences | News

© 2022-2023 Indian Academy of Sciences, Bengaluru.