Calibration of embedded-cluster method for defect studies in amorphous silica

We performed validation and calibration of the embedded-cluster method in order to study its applicability to modeling defects in amorphous silica, where defect models are not well established. As test systems we used well-studied E-4(') and E-1(') centers in alpha-quartz and compared our results with the experimental data and the results of periodic density-functional-theory calculations. Our method can reproduce the essential physics of both centers in good agreement with experiment. The relative energies of different configurations obtained in our calculations are consistent for the two centers and are in qualitative agreement with experiment. The calculated hyperfine parameters agree with the experimental values within 20%. The defect-induced relaxation propagates for more than 10 Angstrom at the puckered side of the E-1(') center. We discuss factors which determine the accuracy of calculations of relative defect energies in crystalline and amorphous silica.