Section Linear Response::Casida
Default all states
The calculation of the excitation spectrum of a system in the Casida frequency-domain formulation of linear-response time-dependent density functional theory (TDDFT) implies the use of a basis set of occupied/unoccupied Kohn-Sham orbitals. This basis set should, in principle, include all pairs formed by all occupied states, and an infinite number of unoccupied states. In practice, one has to truncate this basis set, selecting a number of occupied and unoccupied states that will form the pairs. These states are specified with this variable. If there are, say, 15 occupied states, and one sets this variable to the value "10-18", this means that occupied states from 10 to 15, and unoccupied states from 16 to 18 will be considered.
This variable is a string in list form, i.e. expressions such as "1,2-5,8-15" are
valid. You should include a non-zero number of unoccupied states and a non-zero number
of occupied states.
states/states_elec.F90 : 2568
call parse_variable(namespace, 'CasidaKohnShamStates', default, wfn_list)