Reports: GB6
46824-GB6 Theoretical Investigations of Transition Metal Carbides
Transition metal carbides (TMCs) have received considerable attentions from experimentalists and theoreticians because of their unique physical and chemical properties and exhibit advantages over their parent metals in terms of activity, selectivity, and durability. Our understanding of TMCs is very limited, both experimentally and theoretically. The goal of this project is to supply the reliable theoretical results for the future experimental study.
During this year, investigations were first focused on NiC2. Geometry optimizations were done at the CASSCF level, using a smaller active space including 3d and 4s on Ni and 2s and 2p on O. Douglas-Kroll-Hess (DKH) was applied for the scalar relativistic effect and Multi-reference 2nd order Moller Plesset Perturbation theory (MRMP2) was used for the dynamic electron correlations. Results showed that the relativistic effect and electron correlation are both important in describing the electronic structure of NiC2. In addition, the effect of 3s and 3p was also examined by running the similar MCSCF calculations with a bigger active space, including 3s, 3p, 3d, 4s on Ni and 2s and 2p on O. Due to the computational resources, such calculations could not be done at the CASSCF level. Instead, the incomplete active space approach was applied where the active orbitals are divided into two orbital groups. The first group only contains 3s and 3p on Ni and only single and double excitations from the first group to the second group are considered.
Current studies aim on the similar studies with two analogs, CrC2 and CuC2. Cr has half-filled d orbitals amd Cu has almost fulfilled d orbitals. The calculations have been extending to these two molecules to identify their ground state and low-lying excited states. At the same, the effect of scalar relativistic effect, the dynamic electron correlation, and the size of the active space will be studied and compared with NiC2 in order to find the periodic pattern of the chemical bonding in 3d transition metal dicarbides.
