In this paper, the linear and second order nonlinear optical properties of CsGeX3 (X = Cl, Br, and I) compounds have been investigated using the finite field method combined with the density functional investigation. The obtained results are in good agreement with the experimental values. The electron density distribution nearby the fermi level is the lobe-like lone pair electrons which make the germanium-halogen polyhedron distorted. The atomic contribution to the birefringence and SHG response is analyzed using the Born effective charges, the variation of the atomic charges, and the SHG density method. The results show that the germanium and halogen atoms give main contribution to the optical anisotropic birefringence and the SHG response.
