A first-principles study of formic acid adsorption on CaO (001)

Formic acid adsorption on CaO (001) is analyzed using Density Functional Theory (DFT) with Van der Waals corrections, implemented through the Vienna ab Initio Simulation Package (VASP). Our calculations reveals two possible adsorption sites at low coverage with adsorption energies of -2.38 eV and -2.07 eV. For both sites we found a similar structural behavior, with a considerable elongation of the formic acid O-H bond with respect to the molecular distance. The analysis of the electronic structure and bonding show a stabilization of formic acid as a result of a shift in their states to lower energies, with respect to the gas phase. There is a small charge transfer (0.03 e(-)) from the hydrogen to the surface. At the same time, formic acid oxygens also experiment a charge decrease of 0.15 e(-) and 0.13 e(-), being the ones with the greatest charge variation during the adsorption process.