An analytical potential energy model for ammonia-H 2 from first principle

We construct a set of analytical potential energy models for the interaction of the para-H 2-ammonia, ortho-H 2-ammonia, and classical-H 2-ammonia dimers by fitting a function to a number of ab initio energies. The minimum energy for the classical-H 2-ammonia dimer is at -1.1164 mhartree. The classical-H 2 molecule is the 'hydrogen bond donor' on the side of the lone pair on the nitrogen atom. The minimum energy obtained for the para-H 2-ammonia is -0.289 mhartree, and for ortho-H 2-ammonia is -0.281 mhartree. The ammonia molecule is the hydrogen bond donor in both dimers.