Due to the big calculation effort that is necessary for building a 6D PES including x,y coordinates of the adsorbtion site in the surface plane, by the same method, I consider that a molecular dynamics would allow a more complete description of the phenomena registered folowing the H2 collision with MgO (001) surface (reaction channels, the hydrogens diffusion on the surface and inside MgO).
On the other hand, MD makes possible to consider in a natural manner the influence of the surface temperature upon the channels of scattering/sticking of H2 on MgO (001).
The periodic scheme imposed by the PW formalism (as example the FHI program) allows the simulation of the surface by a SLAB structure, the projectile and the target being included in a large enough 2D supercell to minimize the direct and indirect interactions between the projectiles of two neighbouring supecells.
The introduction of the core pseudopotentials decreases the calculation effort and makes possible to consider a large enough supercell to ensure a small enough H-mass relation to decribe correctly the H2 - surface collision kinetics necessary in describing the mechanisms of energy transfer among the molecule translation and vibration freedom degrees and their coupling to the surface phonone movement. The new types of pseudopotentials permit the tackle of the ionic system in which the electrons are localized.
Therefore, utilization of the MD-SCF-PW programs would allow the study of the surface phenomena in a natural manner. The geometrical optimization methods based on the conjugate gradient technique involve a bigger calculation effort than the dynamic Car Parrinello-type method. The latter is natural within a Kohn Sham scheme based on plane waves.
This mechanism of OH formation is competed by a mechanism of dissociation on the MgO (001) surface with point deffects of the adsorbed or from-volume molecule of H2O.
From an experimental point of view it is difficult to distinguish the OH resulted from the two types of dissociation. Therefore a comparative study of the two types of dissociation is important. The surface hydroxilation and OH diffusion in MgO could be regarded as two preliminary stages before the formation of brucite Mg(OH)2.
Starting from the brucite structure, I intend a futher approach of double-layer hydroxyls (DLH)% % EMBED Equation.2 that have many applications in catalysis and material science.
In order to study these systems the following steps are necessary:
The standadization of the calculation scheme SCF-KS-PW:
- chosing of the local/nonlocal core pseudopotentials;
- chosing of correlation and exchange potentials;
- establishing of the cut-off value of the plane wave energy
by reproducing the volume properties of MgO and of the free molecules H2 and H2O.
The specification of certain shape and size of the surface supercell, so that the direct and indirect interactions between the point deffects of two neighbouring supercells should be minimum.
The relaxation/rumpling of the clean MgO (001) surface and in the presence of point deffects.
The dynamics of H2 and H2O collision with the clean and deffect MgO (001) surface.
The dissociation and reactivity of H2 and H2O and of the dissociation products (H+ and OH-) with substitution atoms or surface-adsorbed atoms.
The penetration of H and OH into the volume as the first step in the formation of the brucite structure.
The structural and electronic characterization of the brucite surface.
The study of the DLH monolayer and tow layer.
The characterization of the DLH interlayer interaction.
My knowledge on the reaction mechanisms of H2 on MgO (001) surface acquired during the elaboration of the PhD thesis and the ability to handle GAMESS, GAUSSIAN (SCF-LCAO-MO), CRYSTAL (SCF-LCAO-CO) and FHI (SCF-KS-PW) programs in Static, Molecular Dynamic and Monte Carlo regime, allow me to successfully fulfill this study plan.