Section Linear Response::Casida
An alternative to CasidaKohnShamStates for specifying which occupied-unoccupied transitions will be used: all those whose eigenvalue differences are less than this number will be included. If a value less than 0 is supplied, this criterion will not be used.
states/states_elec.F90 : 2453
call parse_variable(namespace, 'CasidaKSEnergyWindow', -M_ONE, energy_window, units_inp%energy)