molecular dynamics method
R.R. Zaripov, R.M. Khusnutdinoff
Currently, there is a significant increase in the number of works devoted to the study of the properties of water. Of particular interest in the fluid due to two main factors: the enormous role that water plays in the functioning of various physical, chemical and biological processes, as well as the need to explain the well known anomalous properties of water. Typically, the anomalies of physical properties of water associated with the structure of its molecules, as well as typical water specific type of intermolecular interactions – hydrogen bonds (HB).
In this work, the study of the phase transition «water – amorphous ice» for the water system with TIP5P interaction potential was carry out by computer simulation molecular dynamics.
System under investigation consisted of water molecules arranged in a cubic cell with periodic boundary conditions. For the numerical integration of the equations of motion of particles in the system was used Beeman algorithm with a time step of 10-15 s. All modeling was performed in NpT ensemble with Berendsen thermostat and barostat. Structural characteristics of the system, as well as the configuration of hydrogen bonds were obtained with values of the external pressure: 1, 1000, 2000, 3000, 4000 and 5000 atmospheres. For each value of the pressure system was at the temperature of 300 K, and then rapidly cooled at the rate dT/dt> 1012 K/s, bypassing the crystallization is shown in an amorphous state to the temperature of 200 K.
Based on the results during the numerical experiment data were examined especially changes in the molecular structure and hydrogen-bond network of water at the phase transition. For all thermodynamic states the studied system were calculated partial radial distribution functions, the Wendt-Abraham parameter, the translational order parameter, the average lifetime of hydrogen bonds, the distribution of the number of HB. It was shown the crucial role of hydrogen bonds in explaining the properties and characteristics of water in different thermodynamic states.