Laboratory for Theoretical Solid State Physics, Institute for Materials Research Tohoku University, Aoba-ku, Katahira 2-1-1, Sendai 980-8577, Japan Tel. +81 22 215 2005, FAX +81 22 215 2006
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Theoretical Physics Section, Kavli Institute of NanoScience, TU Delft Lorentzweg 1, 2628 CJ Delft, The Netherlands Tel. +31 15 2784719 FAX +31 15 2781203
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