Quadratic response calculation: *QUADRA

Calculation of third-order properties as quadratic response functions . A,B, and C-named options refer to the operators in the quadratic response function [91, 93, 94]

.SINGLE   Computes the single residue  of the quadratic response function . For the case of dipole operators this corresponds to two-photon transition moments  .

.DOUBLE   Computes the double residue  of the quadratic response function . Double residues of the quadratic repsonse function correspond to transition moments between excited states .

.DIPLEN   Sets A, B, and C to dipole operators .

.DIPLNX   Sets A, B, and C to the x dipole operator .

.DIPLNY   Sets A, B, and C to the y dipole operator .

.DIPLNZ   Sets A, B, and C to the z dipole operator .

.KERR   Only response functions connected to the Kerr effect , , are computed.

.FREQUENCIES  
READ *, NFREQ
READ *, FREQ(1:NFREQ)
Response equations are evaluated at given frequencies . Two lines following this option must contain 1) The number of frequencies, 2) Frequencies. The double residue does not contain frequencies, for the single residue and the Kerr effect only the B-frequency is set, and in other cases both B and C-frequencies are set.

.PHOSPHORESCENCE   Specifies a phosphoresence  calculation, i.e., the spin-orbit  induced singlet-triplet transition . This keyword sets up the calculation so that no further response input is required; the A operator is set to the dipole operators  and the B operator is set to the spin-orbit  operators. [91, 95]

.APROP  , .BPROP  , .CPROP  

Specify the operators A, B, and C. The line following this option should be the label of the operator as it appears in the file AOPROPER.

.ASPIN  , .BSPIN  , .CSPIN  

Spin information for quadratic response  calculations. The line following these options contains the spin rank  of the operators A, B, and C, respectively, 0 for singlet operators and 1 for triplet operators. If .SINGLE RESIDUE   is specified, .CSPIN   denotes the spin of the excited state. If .DOUBLE RESIDUE   is specified, both .BSPIN   and .CSPIN   denote excited state spins. In a triplet response calculations two of these operators are of rank one, and the remaining operator of rank zero.

.BFREQ  , .CFREQ  

The frequencies and . Input as in *LINEAR  .FREQUENCIES  .

.MAXIT   Maximum number of iterations in this section.

.MAXITO   Maximum number of iterations in the optimal orbital  algorithm [7]. Default is 5.

.PRINT  
READ *,IPRINT
Print level.

.SHG   Only response functions connected with second-harmonic generation  are computed, .

.THCLR   Threshold for solving the linear response equations. Default is .

.MAXITP   Maximum number of iterations in solving the linear response  eigenvalue equations.

.THCPP  
READ *, THCPP
Threshold for solving the linear response  eigenvalue equation. Default is .