Nanodiamond Collective Electron States and their Localization
The existence and localization of collective electron states for nanodiamond particles were studied both by solving a one-particle one-dimensional Schrödinger equation in the Kronig-Penney potential and by ab initio computations of ground state wavefunctions of diamondoids C78H64, C123H100 and C211H140 at the DFT R-B3LYP/6-31G(d,p) level of theory. Three distinct classes of collective electron states have been found: collective bonding orbitals resembling the morphology of 3D-modulated particle in a box solutions; surface-localized non-bonding conductive Tamm states and subsurface-localized bonding states for non-uniformly compressed nanodiamond. Quantum-mechanical analysis shows that collective unpaired electrons are intrinsic to nanodiamond. Their subsurface localization is described in terms of surface compression arising from a self-consistency condition of the electron-nuclear wavefunction. Intrinsic spin existence is supposed to result from the collective and spread nature of subsurface orbitals, allowing spin-density fluctuation effects to become significant on this length scale. Suggested model allows to explain free spins of nanodiamond exhibited in experiments.