Insight into the surface activity of defect structure in α-MnO(2) nanorod: first-principles research

The contribution of defect structure to the catalytic property of α-MnO(2) nanorod still keeps mysterious right now. Using microfacet models representing defect structure and bulk models with high Miller index, several parameters, such as cohesive energy, surface energy, density of state, electrostatic potential, et al., have been used to investigate the internal mechanism of their chemical activities by first-principles calculation. The results show that the trend in surface energies of microfacet models follows as E(surface)[(112 × 211)] > E(surface)[(110 × 211)] > E(surface)[(100 × 211)] > E(surface)[(111 × 211)] > E(surface)[(112 × 112)] > E(surface)[(111 × 112)], wherein all of them are larger than that of bulk models. So the chemical activity of defect structure is much more powerful than that of bulk surface. Deep researches on electronic structure show that the excellent chemical activity of microfacet structure has larger value in dipole moments and electrostatic potential than that of bulk surface layer. And the microfacet models possess much more peaks of valent electrons in deformantion electronic density and molecular orbital. Density of state indicates that the excellent chemical activity of defect structure comes from their proper hybridization in p and d orbitals.