Pair-hopping characteristic of lithium diffusive motion in Li-doped beta-phase manganese phthalocyanine

We report a first-principles molecular dynamics study on Li-doped beta-phase manganese phthalocyanine (MnPc). Four electronegative sites next to pyrrole-bridging nitrogen atoms in single MnPc were characterized by analyzing electrostatic potentials. In one-dimensional stacked MnPc, six binding sites were unambiguously located, among which two were newly identified by both static and dynamic simulations. Molecular dynamics simulations were conducted to explore the underlying mechanism governing the diffusive motion of Li dopants. The continuous diffusion of Li atoms among these six binding sites of adjacent MnPc molecules has a distinct cooperative pair-hopping character. The activation energy is significantly lower for pair-hopping than for a single jump.