How or not to calculate Ni(II) Werner-type complexes: evaluation of quantum chemical methods

Atomistic modelling of CVD synthesis of carbon nanotubes and graphene

We discuss the synthesis of carbon nanotubes (CNTs) and graphene by catalytic chemical vapour deposition (CCVD) and plasma-enhanced CVD (PECVD), summarising the state-of-the-art understanding of mechanisms controlling their growth rate, chiral angle, number of layers (walls), diameter, length and quality (defects), before presenting a new model for 2D nucleation of a graphene sheet from amorphous carbon on a nickel surface. Although many groups have modelled this process using a variety of techniques, we ask whether there are any complementary ideas emerging from the different proposed growth mechanisms, and whether different modelling techniques can give the same answers for a given mechanism. Subsequently, by comparing the results of tight-binding, semi-empirical molecular orbital theory and reactive bond order force field calculations, we demonstrate that graphene on crystalline Ni(111) is thermodynamically stable with respect to the corresponding amorphous metal and carbon structures. Finally, we show in principle how a complementary heterogeneous nucleation step may play a key role in the transformation from amorphous carbon to graphene on the metal surface. We conclude that achieving the conditions under which this complementary crystallisation process can occur may be a promising method to gain better control over the growth processes of both graphene from flat metal surfaces and CNTs from catalyst nanoparticles.

Quantum chemical studies on the enantiomerization mechanism of several [Zn(py)3(tach)]2+ derivatives

The enantiomerization mechanism of the trigonal-prismatic [Zn(py)(3)(tach)](2+) complex and several derivatives has been studied by applying DFT calculations (B3LYP/LANL2DZp). The enantiomerization pathways of [Zn(py(3)tach-X)](2+) (X = C, Si, Ge, N, P, As, O, S and Se) start from a distorted trigonal-prismatic C(3) symmetric ground state via an ideal trigonal-prismatic C(3v) structure to end up in a C(3)' symmetric image of the ground state. The activation energy and structural data of the complexes depend on electronic and steric factors. The activation barriers of the complexes decrease in the order [Zn(py(3)tach-Ge)](2+) > [Zn(py(3)tach-Si)](2+) > [Zn(py(3)tach-As)](2+) > [Zn(py(3)tach-Se)](2+) > [Zn(py(3)tach-P)](2+) > [Zn(py(3)tach-S)](2+) > [Zn(py(3)tach-C)](2+) > [Zn(py(3)tach-N)](2+) > [Zn(py(3)tach-O)](2+).