  Kinetics of vacancy defect in graphene drives structural modifications
leading to disorder, multi-vacancy complex and edge reconstruction. Within the
first-principles calculations, we study the dynamic Jahn-Teller distortion and
diffusion of a vacancy defect. Further, the intricate dependence of carrier
doping is systematically investigated. The experimental observation of dynamic
Jahn-Teller distortion is argued to be blocked by defect functionalization and
charge doping. We demonstrate that lattice relaxation perpendicular to the
graphene sheet along with the in-plane strain relaxation plays predominant
roles in predicting the correct microscopic mechanism for vacancy diffusion.
The importance of quantum correction to the classical barrier is discussed. The
calculated activation barrier increases upon both electron and hole doping and
the observed trends are explained by the differential charge density
distribution and hardening of the responsible low-energy phonon modes. Electron
doping essentially freezes the vacancy motion, and thus any degradation
mediated by it. While tracking and analyzing the vacancy diffusion
experimentally in graphene is a difficult task, the present results will
motivate new experimental efforts and assist interpretation of the results.
