DFT study of isocyanate chemisorption on Cu(100) Correlation between substrate-adsorbate charge transfer and intermolecular interactions

The adsorption of isocyanate (-NCO) species on Cu(100) was studied using the density functional theory (DFT) and the periodic slab model. The calculations indicate that at low and intermediate coverages NCO adsorbs preferentially on bridge and hollow sites. Work function and dipole moment changes show a significant negative charge transfer from Cu to NCO. The resulting charged NCO species interact repulsively among themselves being these dipole-dipole interactions particularly intensive when they are adsorbed in adjacent sites. Consequently, isocyanates tend to be separated from each other generating the vacant sites required for the dissociation to N and CO. This condition for NCO dissociation has been suggested in the past from experimental observations. A comparison was also performed with the NCO adsorption on Pd(100). In particular, the calculated minimal energy barrier for NCO dissociation was found to be higher on Cu(100) than on Pd(100) in accord with the well known higher NCO stability on Cu(100). (C) 2011 Elsevier B.V. All rights reserved.