The specification of operators used in solving for response vectors is designed to be very flexible. The general form of the $response input section is given by
$response keyword_1 setting_1 keyword_2 setting_2 ... [operator_1_label, operator_1_origin] [operator_2_label, operator_2_origin] [operator_3_label, operator_3_origin] ... $end
where the keywords are those found in section 11.15.1 (with the exception of RESPONSE).
The specification of an operator is given within a line contained by , where the first element is a label from table 11.4, and the second element is a label from table 11.5. Operator specifications may appear in any order. Response values are calculated for all possible permutations of operators and their components.
For the Cartesian moment operator, a third field within  may be specified for the order of the expansion, entered as . For example, the molecular response to the moment of order (2, 5, 4) with its origin at (0.2, 0.3, 0.4) a.u. can be found with the operator specification
[multipole, (0.2, 0.3, 0.4), (2, 5, 4)]
|dipole or diplen||dipole (length gauge)|
|quadrupole||second moment (length gauge)|
|multipole||arbitrary-order Cartesian moment (length gauge)|
|fermi or fc||Fermi contact|
|spindip or sd||spin dipole|
|angmom or dipmag||angular momentum|
|dipvel||dipole (velocity gauge)|
|zero||Cartesian origin, same as (0.0, 0.0, 0.0)|
|(x, y, z)||arbitrary point (double precision, units are bohrs)|