The Application Of ABEEM-7P Water Models For Molecular Dynamics Simulations Of Water In NPT Ensemble

Molecular dynamics simulations of containing 216 and 500 water molecules in liquid water system which using period boundary condition are run in this paper using ABEEM-7P water models in NVT and NPT ensemble. We study the influence of different NVT 、 NPT ensemble running time; the same temperature relaxation time τT=0.01 ps, different pressure relaxation time of molecular dynamics simulations; the distance of the lone pair electrons of oxygen atoms and hydrogen atoms in different water molecules is closer than which values, it begins to form hydrogen bond, all the impacts on the molecular dynamics simulations. Through the analyses, we find when the NVT ensemble running time is 500 ps, the deviation of simulation dynamic properties and experimental values is smaller than other values and with faster calculation speed. When τT=0.01 ps, τP is larger or smaller, the deviation of dynamic properties is bigger, the distance between the lone pair electrons on the oxygen atoms and hydrogen atoms in different water molecules is less than 1.8 ? begins to form hydrogen bond, the 1.8 ? simulation values are better than the 1.9~2.3 ? and the deviation of simulation values and experimental values is smaller. As a result, the rang of τP is from 0.05 ps~5 ps of molecular dynamics simulations of containing 216 and 500 water molecules, the distance between the lone pair electrons on the oxygen atoms and hydrogen atoms in different water molecules is less than 1.8 ? begins to form hydrogen bond.Application the above research results, this paper analyzes 216 and 500 water molecules in different temperatures range from 260 K~310 K, the same τT and different τP, some dynamic and temperature-dependent properties of NPT ensemble, such as density、pressure、temperature 、dipole moment and so on. The analysis results show, 216 water molecules when τP=0. 5 ps、500 water molecules when τP=5.0 ps, the change of temperature-dependent of density is close to experimental values. When τP=0.05 ps and 0.1 ps, the deviation of the average pressure of 216 and 500 water molecules with target pressure is smaller and fluctuating near 1 atm. The average dipole moment gradually increases with the increase of τP, the values of 216 water molecules are greater than 500 water molecules. As a whole, the dynamic properties of 216 water molecules are better than 500 water molecules, the reason is dispute.In order to further reflect the advantage of ABEEM-7P floating charge models, the molecular dynamics simulations are carried out under the fixed charge model of Amber force field, we analyze the dynamics properties of containing 216 and 500 water molecules in liquid water system under the Amber force field fixed charge models, the results are compared with ABEEM-7P water models. The analyses show that the temperature-dependent and dynamic properties of ABEEM-7P models of containing 216 and 500 water molecules, especially the change of temperature-dependent of density is similar with the experimental values and better than the change trend of Amber force field. This study provides a good reference for further detailed studies of water molecule models.