Ab initio study of ammonia adsorption states on an ice surface I: structures, adsorption energies and linear dependences on coverage ratio

On the (0 0 1) surface of the perfect ice, the ammonia adsorption state has been investigated via ab initio calculations based on the density functional theory (DFT). For the mono- and multilayer adsorption, we obtained a number of optimal structures of ammonia molecules, e.g., the surface bound state. For the monolayer adsorption, it was found that the hydrogen bond length and the adsorption energy depend linearly on the ammonia coverage ratio. For the multilayer adsorption, it is suggested that, in the second ammonia layer, the nitrogen atom of an NH3 molecule would have three hydrogen bonds with three ammonia molecules in the first (or bottom) ammonia layer.