Quadratic response calculation of transition moments between excited states: *QUADRA with .DOUBLE RESIDUE

Calculation of third-order properties as quadratic response functions. $A,B$, and $C$-named options refer to the operators in the quadratic response function $\langle\!\langle A;B,C\rangle\!\rangle_{\omega_b,\omega_c}$ [164,166,167]

.A2TEST Test the contributions to the quadratic response function arising from the $A^{\left[2\right]}$ term. Mainly for debugging purposes.

.DIPLEN Sets $A$ to dipole operators.

.DIPLNX Sets $A$ to the $x$ dipole operator.

.DIPLNY Sets $A$ to the $y$ dipole operator.

.DIPLNZ Sets $A$ to the $z$ dipole operator.

.DIPMAG Sets $A$ and $B$ to angular momentum operators.

.DIPMGX/Y/Z Sets $A$ and $B$ to the X, Y, or Z component of the angular momentum operators.

.DOUBLE RESIDUE Computes the double residue of the quadratic response function. Double residues of the quadratic response function correspond to transition moments between excited states, $\langle B \mid A \mid C \rangle$.

.DIPVEL Sets $A$ and $B$ to the dipole velocity operators.

.DIPVLX/Y/Z Sets $A$ and $B$ to the X, Y, or Z component of the dipole velocity operator, respectively.

.E3TEST Test the contributions to the quadratic response function arising from the $E^{\left[3\right]}$ and $S^{\left[3\right]}$ terms. Mainly for debugging purposes.

.EXMTES Test that the transition moment is symmetric, i.e. that $\left<i\left\vert A\right\vert j\right> = \left<j\left\vert A\right\vert i\right>$. Mainly for debugging purposes.

.IPREXM
READ *,IPREXM
Print level for special excited state transition moment routines.

.ISPABC
READ *, ISPINA,ISPINB,ISPINC
Spin symmetry of $A$-operators (ISPINA) and the left and right excitation operators (ISPINB and ISPINC): "0" for singlet and "1" for triplet. Default is "0,0,0", i.e. all of singlet spin symmetry. Note: triplet operators are only implemented for singlet reference states.

.MAX IT Maximum number of iterations for solving linear response eigenvalue equation in this section.

.MAXITO Maximum number of iterations in the optimal orbital algorithm [22]. Default is 5.

.PRINT
READ *,IPRPP
Print level for solving linear response eigenvalue equations.

.PROPRT

Specify another $A$ operator. The line following this option should be the label of the operator as it appears in the file AOPROPER. This option may be repeated for different property operators.

.QUADMOM Sets $A$ and $B$ to the quadrupole operators.

.QUADXX/XY/XZ/YY/YZ/ZZ Sets $A$ and $B$ to the XX, XY, XZ, YY, YZ, or ZZ component of the quadrupole operator, respectively.

.SPIN-O Sets $A$ and $B$ to spin-orbit operators. Warning: this option implies .TRIPLET and forces the excitations to be of triplet symmetry, and all operators--including e.g. .DIPLEN--will be assumed by the program to be of triplet symmetry!!

.SPNORX/Y/Z Sets $A$ and $B$ to the X, Y, or Z component of the spin-orbit operator, respectively. Warning: this option implies .TRIPLET and forces the excitations to be of triplet symmetry, and all operators--including e.g. .DIPLEN--will be assumed by the program to be of triplet symmetry!!

.THCPP
READ *, THCPP
Threshold for solving the linear response eigenvalue equation. Default is $10^{-3}$.

.X2TEST Test the contributions to the quadratic response function arising from the $X^{\left[2\right]}$ term. Mainly for debugging purposes.