Linear and non-linear optical properties of amorphous Si

We have used the random phase model for the electronic wave-functions to calculate the imaginary part of the dielectric function ε2(ω) and the magnitude of the third-order response, |χ3(ω)| using a model structure of a-Si containing 1728 atoms. We show that this simple calculation gives reasonable results for ε(ω) and furthermore, the behaviour of χ3(ω) is similar to more detailed theoretical calculations.