Geometrical and optical benchmarking of copper(II) guanidine-quinoline complexes: insights from TD-DFT and many-body perturbation theory (part II).

Ground- and excited-state properties of copper(II) charge-transfer systems have been investigated starting from density-functional calculations with particular emphasis on the role of (i) the exchange and correlation functional, (ii) the basis set, (iii) solvent effects, and (iv) the treatment of dispersive interactions. Furthermore (v), the applicability of TD-DFT to excitations of copper(II) bis(chelate) charge-transfer systems is explored by performing many-body perturbation theory (GW + BSE), independent-particle approximation and ΔSCF calculations for a small model system that contains simple guanidine and imine groups. These results show that DFT and TD-DFT in particular in combination with hybrid functionals are well suited for the description of the structural and optical properties, respectively, of copper(II) bis(chelate) complexes. Furthermore, it is found an accurate theoretical geometrical description requires the use of dispersion correction with Becke-Johnson damping and triple-zeta basis sets while solvent effects are small. The hybrid functionals B3LYP and TPSSh yielded best performance. The optical description is best with B3LYP, whereby heavily mixed molecular transitions of MLCT and LLCT character are obtained which can be more easily understood using natural transition orbitals. An natural bond orbital analysis sheds light on the donor properties of the different donor functions and the intraguanidine stabilization during coordination to copper(I) and (II).

Workflow-enhanced conformational analysis of guanidine zinc complexes via a science gateway.

The new science gateway MoSGrid (Molecular Simulation Grid) enables users to submit and process molecular simulation studies on a large scale. A conformational analysis of guanidine zinc complexes, which are active catalysts in the ring-opening polymerization of lactide, is presented as an example. Such a large-scale quantum chemical study is enabled by workflow technologies. Two times 40 conformers have been generated, for two guanidine zinc complexes. Their structures were optimized using Gaussian03 and the energies processed within the quantum chemistry portlet of the MoSGrid portal. All meta- and post-processing steps have been performed in this portlet. All workflow features are implemented via WS-PGRADE and submitted to UNICORE.