Linear Response module written by T. Saue and H. J. Aa. Jensen [Saue2003].

Specification of the A operator
(see *One-electron operators* for details).

Specification of the B operator
(see *One-electron operators* for details).

Specification of both the A and B operators
(see *One-electron operators* for details).

Enforce triangularity of response function.

\[\langle\langle A; B \rangle\rangle_\omega = \langle\langle B; A \rangle\rangle_\omega\]

Only one function is calculated.

*Default:* Deactivated.

Specify frequencies of operator B.

*Example:* 3 different frequencies.

```
.B FREQ
3
0.001
0.002
0.01
```

*Default:* Static case.

```
.B FREQ
1
0.0
```

Employ imaginary frequencies.

Uncoupled calculation.

For each fermion ircop give an *Specification of orbital strings*
of inactive orbitals
to include in the linear response calculation.

For each fermion ircop give an *Specification of orbital strings*
of virtual orbitals
to include in the linear response calculation.

Exclude all rotations between occupied positive-energy and virtual positive-energy orbitals.

Exclude all rotations between occupied positive-energy and virtual negative-energy orbitals.

The user is encouraged to experiment with these options since they may have an important effect on run time.

Specify what two-electron integrals to include
(default: *.INTFLG* under ***HAMILTONIAN*).

Set threshold for convergence before adding SL and SS integrals to SCF-iterations.

*2 (real) Arguments:*

```
.CNVINT
CNVXQR(1) CNVXQR(2)
```

*Default:* Very large numbers.

Set the number of iterations before adding SL and SS integrals to SCF-iterations.

*Default:*

```
.ITRINT
1 1
```

Read solution vectors from file XVCFIL

```
.REAXVC
XVCFIL
```

*Default:* No restart on solution vectors. The file has to have six
characters. Make sure there is no blank character in front of the file
name.

For a restart on solution vectors it is useful to set

```
.REAXVC
XVCFIL
.ITRINT
0 0
```

otherwise LS-integrals (and SS-integrals) are switched on later and one may first iterate away and then back to a possibly converged response vector.

Often you have a converged SCF wave function along with a response vector. In this case make sure that

```
**DIRAC
#.WAVE FUNCTION
```

is commented out. Make then also sure that you use the DFCOEF file which
has been obtained in the *same* calculation as the response vector file.
Otherwise you may observe more response solver iterations than
necessary.

Normalize trial vectors. Using normalized trial vectors will reduce efficiency of screening. CLARIFY!

*Default:* Use un-normalized vectors.

Generate a complete set of trial vector which implicitly allows the explicit construction of the electronic Hessian. Only to be used for small systems !

Only call FMOLI in sigmavector routine: only generate one-index transformed Fock matrix [Saue2003].

Only call FMOLI in sigmavector routine: 2-electron Fock matrices using one-index transformed densities [Saue2003].

Set diagonal elements of orbital part of Hessian equal to

\[-2 m c^2\]

for rotations between occupied positive-energy and virtual negative-energy orbitals.

*Default:* Deactivated.

(Sternheim complement) allows to separate basis set incompleteness from the replacement of an inner sum over negative-energy orbitals only by the full sum. In order to benefit from this functionality (only for specialists !), you should run with print level 2 under properties.

Then you can do a sequence of calculations: 1) .SKIPEP 2) .STERNH 3) .STERNC The diamagnetic contribution of 1) is the non-relativistic expectation value, whereas 2) is the Sternheim approximation, that is replacing orbital energy differences with

\[-2 m c^2\]

With no basis set incompleteness the sum of the diamagnetic contribution 2) and the paramagnetic contribution 3) should equal the diamagnetic contribution of 1).

*Default:* Deactivated.

Reduce number of orbital variation parameters by checking corresponding elements of gradient vector against a threshold. This may reduce memory.

*Default:* No compression.

```
.COMPRESSION
0.0
```

New trial vector will be generated only for variational parameter classes whose residual has a norm that is larger than a fraction 1/RESFAC of the maximum norm.

*Default:*

```
.RESFAC
1000.0
```