a
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
E-mail: andyhor@nus.edu.sg
b
Department of Chemistry, MOE Key Laboratory for Computational Physical Sciences, Fudan University, Shanghai 200433, People's Republic of China
c
Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 3 Research Link, Singapore 117602, Singapore