Structure and Dynamics of Water upon Supercooling

 

Sheeba Malik, Dr. Ananya Debnath

 

Department of Chemistry, Indian Institute of Technology Jodhpur, Jodhpur

 

Water plays a vital role in maintaining the structural integrity of biomolecules, such as, proteins, DNA, membranes. To sequentially understand the dynamics of supercooled bulk and confined water near biomolecules, we investigate dynamical heterogeneities in supercooled water with an all-atom molecular dynamics simulations using TIP4P/2005 water model. We probe the temperature dependence of microscopic structure of TIP4P/2005 water model in terms of radial distribution functions, angular distributions of molecules and tetrahedral order parameters. We find that water molecules have more tetrahedrality as temperature is lowered. Mean square displacement (MSD) show a diffusive to sub-diffusive behavior as temperature is lowered. The non-Gaussian parameter (NGP) show a more prominent β to α relaxation as temperature is lowered revealing glassy dynamics. Self-intermediate scattering function (SISF) of water upon supercooling show two-step relaxations: a fast ballistic and a slow relaxing cage time region, referred to as α-relaxation. Our study will be helpful in understanding the spatio-temporal scale of dynamic heterogeneity of water upon supercooling.

References:

1. Kawasaki, Takeshi; Kim, Kang,;Identifying time scales for violation/preservation of Stokes- Einstein relation in supercooled water,Science Advances,2017,3,8