1. Radiation Effect Analysis Group, Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
2. Riken Harima Institute, Sayo, Hyogo 679-5148, Japan
3. Molecular Modeling and Simulation Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Kizugawa, Kyoto 619-0215, Japan