E' Centers in alpha Quartz in the Absence of Oxygen Vacancies: A First-Principles Molecular-Dynamics Study

The displacement of an oxygen atom in pure alpha quartz is studied via first-principles molecular dynamics. The simulations show that when an O atom in a Si-O-Si bridge is moved away from its original equilibrium position, a new stable energy minimum can be reached. Depending on the spin state and charge Q of the system, this minimum can give rise to either a threefold oxygen (singlet ground state and Q=+1) or to an unsaturated Si atom carrying a dangling bond (triplet state). In the latter case, the hyperfine parameters associated with the Si-29 dangling bond are in rather good agreement with electron paramagnetic resonance/electron nuclear double resonance experiments.