Application of Molecular Orbital Calculations to Fracture Mechanics: Effect of Applied Strain on Charge Distribution in Silica

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Abstract
To further our understanding of the mechanism of environmentally enhanced crack growth, molecular oribital calculations (MO) using the ab initio self‐consistent‐field (SCF) technique have been employed to investigate the effect of applied strain on the atomic charge distribution and the bond overlap population of the Si–O bond at the crack tip of silica. Pyrosilicic acid (H6Si2O7) with eclipsed conformation has been employed as the model molecule. Strain effects up to 20% were simulated in terms of bond stretching and angle distortion. The results indicate that, regardless of how the external strain is applied on the model molecule, the gross electron population on the bridged oxygen increases as strain increases and that on the silicon decreases.