By setting the half-width-at-half-maximum (HWHM) in the lineshape functions equal to the damping factor applied in damped calculations, one obtains identical spectra from resonant and damped response, provided the latter is multiplied by a factor of π -1 . A damping factor of 4.5563 • 10 -3 au (≈ 1000 cm -1 ), as often used in the literature, was applied. The stick spectra were broadened with an HWHM of the same value, unless otherwise stated.