Local structure in lithium chloride solution: a Monte-Carlo simulation study

Monte-Carlo simulations and the nearest neighbour approach have been employed in the present study to investigate the structural properties of aqueous solutions of LiCl salt at ambient conditions. The calculations are performed at increasing concentration of LiCl starting from c = 0.1 m up to 10 m. The analysis shows that increasing salt concentration results in a reduction of the tetrahedral arrangement of water in favour of a non-tetrahedral arrangement characterised by an O-O-O angle between the reference oxygen and two of its four closest oxygen neighbours at 60 degrees. Moreover, the LiCl concentration has a considerable effect on the hydrogen-bonding structure of water. By correctly choosing the nearest neighbours, it is found that the deviation in water structure is due to the presence of chloride ion, not lithium ion, in the first solvation shell of water. It is also demonstrated that in concentrated LiCl solution Cl- ions can substitute the fourth water neighbour which leads to a tetrahedral network formed by water molecules and Cl- ions around a central water molecule. The analysis of the effect of concentration increase on the arrangement of the four closest water molecules neighbours from a reference lithium cation allows us to elucidate a structural maker role of Lithium ion.