Neutron reflectivity and computer simulation studies of self-assembled brushes formed by centrally adsorbed star polymers

The equilibrium properties of polymer brushes formed by starlike polymers with varying number of arms attached to a surface by their center were studied experimentally with neutron reflectrometry (NR). Polystyrene (PS) stars in a good solvent (toluene) were centrally adsorbed onto a quartz substrate via a zwitterionic anchor group. Increasing the number of arms resulted in significantly lower equilibrium adsorbance, while replacement experiments of a 3-armed star brush by linear chains revealed interesting equilibrium and kinetic features related to the special architecture of star polymers. These results are compared with scaling theoretical calculations and Monte Carlo simulations of centrally adsorbed star polymers that were performed under the bond fluctuation simulation scheme. Several features of the experimental results are reproduced in our simulation study. © 2008 American Chemical Society

A self-consistent, relativistic implementation of the LSDA plus DMFT method

V tomto prehľadovom článku ukazujememe nový vývoj metódy LSDA+DMFT tak ako je naimplementovaná v KKR metóde. Okrem formalizmu sa zameriame na niekoľko príkladov a aplikácii tejto metódy ako napr GaMaAs, ARPES a magntický Comptov profilIn this review we report on developments and various applications of the combined Density Functional and Dynamical Mean-Field Theory, the so-called LSDA + DMFT method, as implemented within the fully relativistic KKR (Korringa-Kohn-Rostoker) band structure method. The KKR uses a description of the electronic structure in terms of the single-particle Green function, which allows to study correlation effects in ordered and disordered systems independently of its dimensionality (bulk, surfaces and nano-structures). We present self-consistent LSDA+DMFT results for the ground state and spectroscopic properties of transition metal elements and their compounds. In particular we discuss the spin-orbit induced orbital magnetic moments for Fex Ni1−x disordered alloys, the magnetic Compton profiles of fcc Ni and the angle-resolved photoemission spectroscopy (ARPES) spectra for gallium manganese arsenide dilute magnetic semiconductors. For the (GaMn)As system a direct comparison with the experimental ARPES spectra demonstrates the importance of matrix element effects, the presence of the semi-infinite surface and the inclusion of layer-dependent self-energies