Variationally Calculated Vibrational Energy Levels of Ammonia Adsorbed on a Ni(111) Surface

We have calculated vibrational energy levels for an ammonia molecule adsorbed on a Ni(111) surface. An exact kinetic energy operator for the gas phase molecule is combined with a potential energy function that is calculated with the plane-wave density-functional theory. The resulting eigenvalue problem is solved variationally. The vibrational energy levels for a gas phase molecule are also calculated. The calculated adsorption-related shift is +193 cm −1 for the symmetric bend, −54 cm −1 for the asymmetric bend, −68 cm −1 for the symmetric stretch, and −63 cm −1 for the asymmetric stretch, in good agreement with the experimental values +190, −47, −67, and −84 cm −1, respectively.