# *EXCITATION ENERGIES¶

Calculate excitation energies using time dependent Hartree-Fock or DFT. The excitation energies are found as the lowest generalized eigenvalues of the electronic Hessian. DIRAC supports TDDFT kernels from all ground state functionals included in the code. Currently the iterative eigenvalue solver may fail to converge more than about twenty roots per symmetry.

## Define excitations and transition moments¶

### .EXCITA¶

```
.EXCITA
SYM N
```

Number of excitation energies N calculated in boson symmetry no. SYM. This keyword can be repeated if you want excitation energies in more than one boson symmetry.

### .OPERATOR¶

Specification of a transition moment operator (see
*One-electron operators* for details). This keyword can be given multiple
times to add more operators.

### .EPOLE¶

Specification of electric Cartesian multipole operators of order L for the calculation of transition moments. Specify order.

*Example:* Electric dipole operators

- ::
- .EPOLE 1

### .MPOLE¶

Specification of magnetic Cartesian multipole operators of order L for the calculation of transition moments. Specify order.

*Example:* Magnetic dipole operators

- ::
- .MPOLE 1

### .ANALYZE¶

Analyze solution vectors and show the most important excitations at the orbital level.

### .INTENS¶

Invoke calculation of oscillator strengths. Followed by oscillator strengths to order k in the wave vector, which must be zero.

*Example:*

```
.INTENS
0
```

## Control variational parameters¶

### .OCCUP¶

For each fermion ircop give an *Specification of orbital strings* of inactive orbitals from
which excitations are allowed. By default excitations from all occupied
orbitals are included in the generalized eigenvalue problem.

Example:

```
.OCCUP
1..3
7,8
```

This would include excitations from gerade orbitals 1,2,3, and ungerade orbitals 7 and 8.

### .VIRTUA¶

For each fermion ircop give an *Specification of orbital strings*
of virtual orbitals
to which excitations are allowed. By default excitations to all virtal
orbitals are included in the generalized eigenvalue problem.

### .SKIPEE¶

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

### .SKIPEP¶

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

## Control reduced equations¶

## Control integral contributions¶

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

### .INTFLG¶

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

### .CNVINT¶

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.

### .ITRINT¶

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

*Default:*

```
.ITRINT
1 1
```

## Advanced/debug flags¶

### .E2CHEK¶

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

### .ONLYSF¶

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

### .ONLYSG¶

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