Cluster and periodic DFT calculations of MgO/Pd(CO) and MgO/Pd(CO)2 surface complexes

The bonding and vibrational properties of Pd(CO) and Pd(CO)(2) complexes formed at the (100) surface of MgO have been investigated using the gradient-corrected DFT approach and have been compared to the results of infrared and thermal desorption experiments pet-formed on ultrathin MgO films. Two complementary approaches have been used for the calculation of the electronic properties: the embedded cluster method using localized atomic orbital basis sets and supercell periodic calculations using plane waves. The results show that the two methods provide very similar answers, provided that sufficiently large supercells are used. Various regular and defect adsorption sites for the Pd(CO) and Pd(CO)(2) have been considered: terraces, steps, neutral and charged oxygen vacancies (F and F+ centers), and divacancies. From the comparison of the computed and experimental results, it is concluded that the most likely site where the Pd atoms are stabilized and where carbonyl complexes are formed are the F+ centers, paramagnetic defects consisting of a single electron trapped in an anion vacancy.