Fig. 2
From: Giant non-linear susceptibility of hydrogenic donors in silicon and germanium
Contributions to C(3) from the resonant and anti-resonant terms for hydrogen: 〈ψ0|ζG3ζG2ζG1ζ|ψ0〉 (blue), 〈ψ0|ζG−1ζG2ζG1ζ|ψ0〉 (yellow), 〈ψ0|ζG−1ζG−2ζG1ζ|ψ0〉 (green), and 〈ψ0|ζG−1ζG−2ζG−3ζ|ψ0〉 (red). At ω = 0, the two terms containing G−2 have opposite signs to the two terms with G2, and the sum tends to 222
