Energiejustierte ab-initio-Pseudopotentiale für mehrkernige Systeme
The effectiveness of the available atomic pseudopotentials (also known as effective core potentials) and their corresponding basis sets is firstly demonstrated through application in quantum chemical ab-initio calculations. Excitation and ionization energies of atoms of group 8 (Fe, Ru, Os) can be calculated without too much effort to within a few tenths of an electron volt, if electron correlation is properly included. Then the first few members of the homologous series of the
... he α,α'-oligothiophenes are studied with a variety of quantum chemical standard methods. Reliable data for various physical properties can be obtained again also in this study, where a superposition of atomic pseudopotentials simulates the effect of the atomic cores of all non-hydrogen atoms on the remaining, explicitly treated valence part. This behaviour could not be expected from the outset. It is then shown how group pseudopotentials (pseudopotentials for multinuclear systems, like molecular fragments, ligands, substituents or even complete molecules) can be generated in a general way. The method is tested for the planar molecules ethene, cyclopentadienyl and benzene, such that the group pseudopotential replaces the system of σ-bonds. It is demonstrated that an energy-adjustment of the parameters in the group pseudopotential can be achieved, despite of problems unknown from the parameter adjustment for atomic pseudopotentials. The benzene-hydrogenchloride complex, C6H6 · HCl, is studied as a first application of a group pseudopotential that was designed to simulate the σ-bonds in benzene. The approach developed here may be used to generate group pseudopotentials for, e.g., methyl, phenyl or amino groups, or for solvent molecules.