First-principles investigation of the adsorption of the 2,5-pyridine di-carboxylic acid onto the Cu(011) surface.

First-principles calculations within the density functional theory (DFT) framework have been performed in order to investigate various conformations of the 2,5-pyridine di-carboxylic acid (PDCA) molecule adsorbed onto the Cu(011) surface. By means of DFT calculations the adsorption geometry, the bond formation and the electronic properties of PDCA molecule conformations on the Cu(011) surface have been studied. The most important structural property is the orientation of the COOH H atom which can point either toward the aromatic ring or toward the vacuum. This H atom position determines the possible reactions in which the adsorbed molecule can get involved and also has a significant impact on the value of the Cu-molecule system work function. Thus, we find that simply by changing the H atom orientation (from up to down) the Cu-molecule system work function can be varied with more than 2.5 eV. This is a significant result as a lot of effort is put nowadays in finding efficient ways for the in situ variation of the systems work function. Scanning tunneling microscopy (STM) images, reflexion absorption infrared vibrational spectra (RAIRS) as well as various thermodynamic properties (adsorption entropies, enthalpies) have also been investigated in order to get a better insight into the system studied and to provide support to possible experimental studies (STM or RAIRS experiments).