Cubic response calculation: *CUBIC

Calculation of fourth-order properties as cubic response functions [169,170,90]. $A,B$,$C$, and $D$-named options refer to the operators in the cubic response function $\langle\!\langle A;B,C,D\rangle\!\rangle_{\omega_b,\omega_c,\omega_d}$

.APROP, .BPROP, .CPROP, .DPROP

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

.BFREQ, .CFREQ, .DFREQ

The frequencies $\omega_b$, $\omega_c$, and $\omega_d$, respectively. Input as in .FREQUE.

.DC-SHG Only response functions connected to the static electric field-induced second harmonic generation are computed, $\gamma(-2\omega;\omega,\omega,0)$.

.DC-KERR Only response functions connected to the static electric field induced Kerr effect are computed, $\gamma(-\omega;\omega,0,0)$.

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

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

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

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

.FREQUE
READ *, NFREQ
READ *, FREQ(1:NFREQ)
Sets the frequencies whenever a optical process is specified. Can also be used for the residue calculation and in which case both $\omega_b$ and $\omega_c$ for the single residue and only $\omega_b$ for the double residue.

.IDRI Only response functions connected to the intensity dependent refractive index are computed, $\gamma(-\omega;\omega,-\omega,\omega)$.

.INVEXP Solve the linear set of equations for the second-order perturbed wave function through explicit matrix inversion. Mainly for debugging purposes.

.ISPABC
READ *, ISPINA,ISPINB,ISPINC
Spin symmetry of $A$, $B$, $C$, and $D$-operators (ISPINA/B/C/D), "0" for singlet and "1" for triplet. Note that currently only singlet triplet response functions have been implemented. Do not use.

.MAX IT Maximum number of iterations for solving linear equations, default value is 60.

.MAXITO Maximum number of optimal orbital trial vector microiterations, default value is 5.

.PRINT Print flag for output, default value is 2. Timer information is printed out if print flag greater than 5. Response vectors printed out if print flag greater than 10.

.THCLR Threshold for convergence of response vectors, default value is $10^{-3}$.

.THG Only response functions connected to the third harmonic generation are computed, $\gamma(-3\omega;\omega,\omega,\omega)$ [171].

.THRNRM Threshold for norm of property vector $X^{[1]}$ to be considered to be greater than zero in order to solve the linear equation
$\left( E^{[2]} - S^{[2]} \right)N^{X} = X^{[1]}$, default value is $10^{-9}$.