Section Linear Response::Polarizabilities
This block describes the multiples of the frequency used for the dynamic hyperpolarizability. The results are written to the file beta in the directory for the first multiple. There must be three factors, summing to zero: $\omega_1 + \omega_2 + \omega_3 = 0$. For example, for second-harmonic generation, you could use 1 | 1 | -2.
sternheimer/em_resp.F90 : 894
if (parse_block(sys%namespace, 'EMHyperpol', blk) == 0) then