1Institut für Physik, Universität Augsburg, 86135 Augsburg,
Germany;
2ICCMP, Universidade de Brasilia, 70904-970 Brasilia, Brazil;
udo.schwingenschloegl (at) physik.uni-augsburg.de
Received 30 April 2008, accepted 16 May 2008 by U. Eckern
Institut für Physik, Universität Augsburg, 86135 Augsburg, Germany;
christopher.mosely (at) physik.uni-augsburg.de / klaus.ziegler (at) physik.uni-augsburg.de
Received 11 July 2007, revised 31 March 2008, accepted 20 May 2008 by U. Eckern
Institute of Theoretical Physics, University of Zürich, 8057 Zürich,
Switzerland; norbert.straumann (at) gmail.com
Received 25 May 2008, accepted 27 May 2008 by A. Wipf