Understanding Relaxation Dynamics of Supercooled Liquid Water from Molecular Dynamics Simulation
Mahabir Prasad and Somendra Nath Chakraborty*
Department of Chemistry, Sikkim University, Gangtok, Sikkim, 737102
mahiraj010[at]gmail.com,*snchakraborty[at]cus.ac.in
Abstract
When liquid water is sufficiently cooled it's thermodynamic response functions like isothermal compressibility, isobaric heat capacity and coefficient of thermal expansion increases sharply and becomes much more pronounced at lower temperatures. This anomalous behaviour of liquid water is of great interest to scientists and till date no clear picture has been sorted out [1]. Study of supercooled liquid water will also enhance our understanding of its occurrence in clouds where it plays an important role in the processing of solar and terrestrial energy fluxes [2]. Supercooled liquid water is important for life at subfreezing conditions and for the commercial preservation of protein and cells. It is observed that in supercooled conditions structural arrangement of water molecules and its relaxations play an important role in determining its thermodynamic and dynamic properties [1]. We perform Molecular Dynamics (MD) Simulations of 2048 water molecules with periodic boundary conditions in isothermal-isobaric (NPT) ensemble and study the relaxation dynamics of several structural properties. Water molecules are modeled using TIP4P/2005 potential and simulations are carried out in the temperature range 280-200 K and at 1 and 1000 bar. Structural properties of water molecules in the first coordination shell is then analysed using bond-orientational and four body order parameters. Auto-correlation functions of these structural properties along with hydrogen bond energy, distance etc. are also obtained. Relaxation times for each of these properties are estimated, compared and then analysed in detail.
References
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2. F. Franks, Water: A Matrix of Life, 2nded., Royal Society of Chemistry, Cambridge, UK (2000); P. Ball, Life's Matrix: A Biography of Water, Farrar, Straus, and Giroux, New York (2000).