Electron Transfer from Hydrogen Molecule to Au(111) During Dissociative   Adsorption: A First-Principles Study
  We investigate the electron transfer from a dissociatively adsorbed H2 molecule to a Au(111) surface using the first-principles methods. A fractional electron transfers from a molecule to a substrate, and potential energy increases during the process. The initial energy increase coincides with that of the isolated, separated, and positively charged H2 molecule calculated by the real-space density functional method. The barrier formation is due to the destabilization of the molecule induced by the electron transfer. The electronegativity difference between the adsorbate and the substrate determines the direction of the electron transfer. 
Shigeyuki Takagi, Jun-ichi Hoshino, Hidekazu Tomono, and Kazuo   Tsumuraya