Carl-Wilhelm Schläpfer

Poly(ethylene imine)-controlled calcium phosphate mineralization

The current paper shows that poly(ethylene imine) (PEI) is an efficient template for the fabrication of spherical calcium phosphate (CaP)/polymer hybrid particles at pH values above 8. The polymer forms spherical entities, which contain one or a few CaP particles with diameters of ca. 6 nm. The samples contain up to 20 wt % polymer, which appears to be wrapped around the small CaP particles. The particles form via a mineralization-trapping pathway, where at the beginning of the precipitation small CaP particles form. Further particle growth is then prevented by precipitation of the PEI onto these particles at pH values of ca. 8. Stabilization of the particles is provided by the re-protonation of the PEI, which is adsorbed on the CaP particles, during the remainder of the mineralization process. At low pH, much larger particles form. They most likely grow via heterogeneous nucleation and growth on existing, polymer-modified CaP surfaces.

Density functional theory study of the Jahn-Teller effect in cobaltocene*

A detailed discussion of the potential energy surface of bis(cyclopentadienyl)cobalt(II), cobaltocene, is given. Vibronic coupling coefficients are calculated using density functional theory (DFT). Results are in good agreement with experimental findings. On the basis of our calculation there is no second-order Jahn–Teller (JT) effect as predicted by group theory. The JT distortion can be expressed as a linear combination of all totally symmetric normal modes of the low-symmetry, minimum-energy conformation. The out-of-plane ring deformation is the most important mode. The JT distortion is analyzed by seeking the path of minimal energy of the adiabatic potential energy surface.

A novel density functional study of the ground state properties of a localized trinuclear copper(II,II,III) mixed-valence system.

Herein we report the analysis of a mixed-valence localized trinuclear copper(II,II,III) cluster by density functional theory. We focused on two peculiar aspects of this system. First we investigated the triplet ground state potential energy surface on a model system. To this end we computed, on the [E multiply sign in circle e] adiabatic potential energy surface, the potential energy profile along the e mode and constructed ab initio the full potential energy surface (the so called Mexican hat), by a fitting procedure. Next, we analyzed the magnetooptical properties of the minimum energy structures. In particular, we applied the single determinant method to compute the full manifold of states arising from the highest occupied molecular orbitals (magnetic orbitals). This procedure yielded results in agreement with previous calculations and with the available experimental data when using a model closer to the X-ray structure or when directly dealing with the complete structure of the system.

A New Method to Describe the Multimode Jahn–Teller Effect Using Density Functional Theory

A new method for the analysis of the adiabatic potential energy surfaces of Jahn–Teller (JT) activemolecules is presented. It is based on the analogy between the JT distortion and reaction coordinates. Within the harmonic approximation the JT distortion can be analysed as the linear combination of all totally symmetric normal modes in the low symmetry minimum energy conformation. Contribution of the normal modes to the distortion, their energy contribution to the JT stabilisation energy, the forces at high symmetry cusp and detailed distortion path can be estimated quantitatively. This approach gives direct insight into the coupling of electronic structure and nuclear displacements. Further more, it is reviewed how multideterminental DFT can be applied for the calculation of the JT parameters. As examples the results for VCl4, cyclopentadienyl radical and cobaltocene are given.