Density functional theory and applications within catalysis and material science

A detailed knowledge of the electronic and geometric structure, as well as relevant reaction mechanisms, is of general interest within material science. With accurate quantum mechanical calculations based on density functional theory (DFT), one can address several issues within e.g. catalysis and surface science.


Homogeneous catalysis

In connection with zirconocene based polymerization of olefins, triphenyl based compounds and ions can be used to study ion pair formation by in situ IR spectroscopy. Observed vibrational spectra may be compared with calculated frequencies, and assignment of the observed IR bands is facilitated by inspection of the calculated normal modes.

 

Figure 1

Figure 1

Figure 1: Ph3CCl (left) and its IR spectrum (right) as calculated with DFT within the harmonic approximation. (O.K. Eide, M. Ystenes, J.A. Støvneng, J.L. Eilertsen)

Surface physics

The chromium oxide surface has applications within catalysis and corrosion resistance. The (0001) surface may terminate with a chromium or an oxygen layer, and in the latter case, the surface oxygen atoms may have single (Cr-O-Cr) or double (Cr=O) bonds to chromium. Adsoption sites and binding energies have been determined for several atoms and small molecules, such as H2, HCl, and Cl2. Dissociation energy barriers typically lie in the range 4 - 6 eV. The figure illustrates the transition state for dissociation of Cl2on the oxygen terminated surface (Cl: yellow, O: red, Cr: blue). This particular reaction is accompanied by substantial surface reconstruction.

Figure 2

Figure 2: Transition state for dissociation of Cl2on an oxygen terminated surface of Cr2O3, as calculated with density functional theory. (K. Nielsen, Ø. Borck, K. Nigussa, J.A. Støvneng)

Parametrization of a reactive force field

When the target is the dynamics of large, reactive systems, quantum mechanical methods like DFT are computationally too expensive. An alternative, then, is to construct an empirical force field which allows breaking and forming chemical bonds; a so-called reactive force field. Accurate DFT calculations are initially performed on small molecular systems and perfect crystals, and the DFT results are used as input for parametrization of the force field. The resulting force field may then be used in molecular dynamics investigations of systems that are too large for DFT calculations. Systems of interest are e.g. III-V and group IV semiconductors, with applications in novel solar cell materials.

Figure 3

Figure 3

Figure 3: Bond breaking in AsH3AlH2AsH2AlH3, as calculated with DFT. (As: red, Al: purple) The aim is to construct an empirical reactive force field that is able to reproduce the DFT results with good accuracy, at a fraction of the computational cost. (J.A. Støvneng, P.O. Åstrand, O. Frisk, M. Søby)

Contact: Jon Andreas Støvneng