# *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.

### .ANALYZE¶

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

## 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¶

### .MAXITR¶

Maximum number of iterations.

Default:

.MAXITR
30

### .MAXRED¶

Maximum dimension of matrix in reduced system.

Default:

.MAXRED
200

### .THRESH¶

Threshold for convergence of reduced system.

Default:

.THRESH
1.0D-5

## 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

### .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].