The solvation structure of lithium ion in water-ammonia mixture by Monte Carlo method

Abstract

The solvation structure of lithium ion in 18.45 mole % aqueous ammonia at 20ºC is investigated, using the Metropolis Monte Carlo method, The system consists of 202 particles, one lithium ion, 37 ammonia and 164 water molecules. The experimental density of 18.45 mole % aqueous ammonia (0.9307 g.cmˉ³) was used, leading to a periodic sidelength of 18.56 Å and half of this length was chosen as spherical cut-off. Five pair potential functions, based on ab into calculations, are used in order to represent all pairs of interactions, four of them were taken from the literatures while the lithium ion/ammonia pair potential was newly constructed in this work. The results show that lithium ion is preferentially solvated by water molecule. There are 4 water and 2 ammonia molecules in the first shell of lithium ion, the second one 8 water and 4 ammonia molecules. The fully solvated lithium ion in 18.45 mole % aqueous ammonia can be characterized by Li[H₂O)₄(NH₃)₂]Ꮖ [(H₂O)₈(NH₃)₄]ᏆᏆ. Distribution of coordination numbers and binding energies have been discussed with respect to exchange mechanisms.