Pan et al. Nanoscale Research Letters 2011, 6:97 http://www.nanoscalereslett.com/content/6/1/97 Page 6 of 7 Figure 7 Calculated PDOSs of two neighboring Cr atoms in Cr-functionalized g-C3N4-zz4. The Fermi level is shifted to 0 eV (dot-dash line). that the d electrons of TM atoms (Cr, Mn, Co, and Ni) are spin-polarized, but the magnetic moments belonging to two neighboring atoms are anti-parallel, resulting in the anti-ferromagnetism (Figure 7). Conclusions In summary, we studied the magnetic properties of metal-functionalized graphitic carbon nitride nanotubes based on the first-principles calculations. The results show that magnetic properties strongly depend on the coupling between the d electrons of metal atoms and p electrons of C or N atoms. The coupling and hybridi- zation between the spin-polarized d electrons of W or Ti atoms and p electrons of C and N atoms result in the ferromagnetic W- and Ti-functionalized nanotubes. Although the d electrons of Cr, Mn, Co, and Ni atoms are spin-polarized, the functionalized nanotubes are anti-ferromagnetic because the spin-polarized d elec- trons are anti-parallel due to lack of coupling. The fer- romagnetic nanotubes may be used in spintronics and other magnetic devices. The functionalized nanotubes may also find potential applications, such as hydrogen and energy storage [36-38]. Abbreviations CBB: conduction band bottom; DMSs: dilute magnetic semiconductors; g- C3N4: graphitic carbon nitride; PAW: projector augmented wave; PDOS: partial density of states; TM: transition metal; VASP: Vienna ab initio simulation package; VBT: valence band top. Acknowledgements This work was supported by the Visiting Investigator Program “Size Effects in Small Scale Materials” hosted at the Institute of High Performance Computing of the Agency for Science, Technology and Research (A*STAR) in Singapore. 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