1. Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan, Research Institute for Computational Sciences (RICS), National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 2, Umezono 1-1-1, Tsukuba 305-8568, Japan, and Dr. Vijay Kumar Foundation, 45 Bazaar Street, K. K. Nagar (West), Chennai 600 078, India