Computational Modelling of Structure and Catalytic Properties …
317
Fig. 1 Example cluster (top) and periodic [4] (bottom) models of Cr(VI) oxide species on silica. In
the first case, the two-layer ONIOM method is applied (the wireframe part of the model represents
the outer layer)
In the case of the periodic models, the surface of the solid is represented by a slab
inside the unit cell that is repeated using periodic boundary conditions (Fig. 1) [1]. For
realistic description of the catalyst surface, especially for amorphous materials, the
unit cell should be large enough to avoid artificial periodicity and lateral interactions
between a surface metal site or adsorbed reactant and its periodic images. Several
advanced slab models of amorphous silica were developed from DFT calculations
[12–16], and some of them were used in computational studies presented below.
317
Fig. 1 Example cluster (top) and periodic [4] (bottom) models of Cr(VI) oxide species on silica. In
the first case, the two-layer ONIOM method is applied (the wireframe part of the model represents
the outer layer)
In the case of the periodic models, the surface of the solid is represented by a slab
inside the unit cell that is repeated using periodic boundary conditions (Fig. 1) [1]. For
realistic description of the catalyst surface, especially for amorphous materials, the
unit cell should be large enough to avoid artificial periodicity and lateral interactions
between a surface metal site or adsorbed reactant and its periodic images. Several
advanced slab models of amorphous silica were developed from DFT calculations
[12–16], and some of them were used in computational studies presented below.