Collaborative Research Centre 546

"Structure, Dynamics and Reactivity of Aggregates of Transition Metal Oxides"

Project A1
 

General information
   

Title:

Quantum chemical calculations of the electronic structure and reactivity of mono- and bicentered vanadium oxide clusters

Research areas:

Theoretical chemistry, quantum chemistry

Leader:

Prof. Dr. Christoph van Wüllen Technische Universität Berlin, Sekr. C3 Institut für Organische Chemie Straße des 17. Juni 135 10623 Berlin Telefon: 030 314 27870 Telefax: 030 314 23727 E-Mail-Adresse: Christoph.vanWullen@tu-berlin.de

Abstract: Our investigations try to predict the chemical reactivity of small vanadium oxide clusters by high-level ab initio calculations. This not only requires accurate energetic data but also an overview as complete as possible over the relevant potential energy surfaces. The results are of particular interest since the largest part of theoretical calculations in this area is restricted to density functional methods which have not been parametrized for this field. Calibration and validation of density functional methods requires quantum chemical reference data with high accuracy. The most accurate current quantum chemical methods require that Hartree-Fock is a good first order approximation to the electronic wave function. This condition is generally not fulfilled for transition metal compounds and is in particular violated when chemical reactions with bond-breaking and bond-making are to be investigated. The quantum chemical work-horse in our project are therefore multireference configuration interaction (MR-CI) calculations and variants thereof such as MR-ACPF and MR-AQCC. Because the dynamical correlation energy converges very slowly with respect to the basis set size, we use extrapolation techniques based on correlation consistent basis sets. These calculations are too demanding to scan whole potential energy surfaces. Therefore we locate interesting molecular structures (energy minima and transition states) with density functional methods and perform MR-CI calculations only for these structures. We have to look at states of different spin multiplicites to locate "best" reaction paths. So far it has become clear the the choice of the active space of the CASSCF reference function is a critical issue that requires extensive testing. So far we have looked at the activation of small alkanes by small vanadium oxide clusters (e. g. methane and the VO cation). Now we want to extend these investigations to larger vanadium oxide clusters with more than one vanadium atom, and at variants thereof in which a vanadium atom is substituted by atoms such as silicon or phosphorous. We also expect to find new reaction channels for these systems (e. g. activation of a C-H bond by one vanadium centre while a hydrogen atom is transferred to another vanadyl group).

 

Publications