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 10.13.2 (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 10.4, and the second element is a label from table 10.5. 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 (i,j,k). 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)]
| Operator Label | Description | Integral |
|---|---|---|
| dipole or diplen | dipole (length gauge) | ⟨χμ|𝐫O|χν⟩ |
| quadrupole | second moment (length gauge) | ⟨χμ|𝐫𝐫T|χν⟩ |
| multipole | arbitrary-order Cartesian moment (length gauge) | ⟨χμ|xiyjzk|χν⟩ |
| fermi or fc | Fermi contact | 4πge3⟨χμ|δ(𝐫K)|χν⟩ |
| spindip or sd | spin dipole | ge2⟨χμ|3𝐫K𝐫TK-r2Kr5K|χν⟩ |
| angmom or dipmag | angular momentum | ⟨χμ|𝐋O|χν⟩ |
| dipvel | dipole (velocity gauge) | ⟨χμ|∇|χν⟩ |
| Origin Label | Description |
|---|---|
| zero | Cartesian origin, same as (0.0, 0.0, 0.0) |
| (x, y, z) | arbitrary point (double precision, units are bohrs) |