A first principles investigation of water dipole moment in a defective continuous hydrogen bond network

摘要

First principles molecular dynamics simulations of an aqueous solution salt system at finite concentration containing both Na+ and Cl- ions show that a change in the distribution of the molecular dipole moment of H2O monomers appears when ions are present in solution. Simulations suggest a lowering of the dipole moments of the water molecules in the solvation shells of Na+ and Cl- as compared to the pure water case, while the dipoles of the rest of the molecules are hardly affected. However, finer analysis in terms of the Wannier centers distribution suggests a change in the electronic structure of the water molecules even in the bulk. Also a change of the H-bond network arrangement was found and correlation between dipole and MOH parameter evidences such subtle effects, suggesting a lowering of tetrahedral order in salty solutions. All these changes can be related to observable quantities such as the infrared spectra thus allowing for a rationalization of the experimental outcome on neutral aqueous solutions.