Photoelasticity of alpha-quartz from first principles

Using density-functional perturbation theory with a scissor correction, we compute the entire photoelastic tensor of alpha -quartz. Its components, whose absolute values range between 0.047 and 0.29 are all described within 0.04. We also compute the Born effective charge tensor and present its variation with respect to strain, as well as the relative deformation potentials and the structural rearrangement caused by strain. Then, we discuss briefly the mechanisms involved in the photoelasticity of quartz.