Pressure and temperature dependence on the hydrogen bonding and dynamics of ammonium ion in liquid water: A molecular dynamics simulations study

Hydrogen-bond properties and dynamics of NH4+ in aqueous solution are calculated at seven different temperatures and pressures by classical molecular dynamics simulations. It is found that NH4+ forms a strong hydration shell in aqueous medium having maximum number of four hydrogen bonds with water molecules. The self-diffusion coefficient of NH4+ decreases in ambient water, whereas in supercooled temperatures the value increases with pressure. Correspondingly, a faster rotational dynamics of NH4+ is observed with the application of pressure at T = 258 K. The effect of pressure on the lifetime of NH4+-water hydrogen-bond is also showing a faster decay compared to water-water hydrogen-bond. The temperature dependence lifetime of NH4+-water hydrogen-bond is found to show Arrhenius-behavior with comparably lower activation energy than the water-water hydrogen-bond. (C) 2013 Elsevier B.V. All rights reserved.