## xc

Specify details associated with the evaluation of the exchange–correlation (xc) kernel.

**Input block**

**Short variant**

```
xc:
[functional]
```

**Extended variant**

`xc:`

`functional: [functional]`

`noncollinearity: [string]`

**Default**

```
xc:
functional : from-scf
noncollinearity : v2019
```

**Example**

`xc: XALDA`

```
xc:
functional : XALDA
noncollinearity : v2005
```

### Warning

- The use of ALDA or XALDA options is not recommended, because they usually approximate the full xc kernel. Their use is only recommended when comparing the calculated data to implementations in other quantum chemistry programs, where those approximations can not be avoided.

## eri

Specify details associated with the evaluation of electron repulsion integrals (ERI) and related two-electron Fock contributions.

## grid

Specify atomic grids for the numerical evaluation of exchange-correlation DFT contributions.

**Input block**

**Short variant**

```
grid:
[grid]
```

**Extended variant**

`grid:`

`all: [string]`

`[element-symbol]: [string]`

`[element-index]: [string]`

`...`

**Default**

`Grid defaults are taken from the SCF section.`

**Example**

`grid: large`

```
grid:
C: medium
7: large
```

### Note

- There can be multiple instances of element-symbol and element-index in the grid block.

- While lines in the grid block can be mixed, they are always processed in the following order: "all", all "element-symbol" and all "element-index" keywords.

- The order of processing the data matters, since the latter lines rewrite the data of the former lines. This way one can easily set the same grid for all Carbons except the Carbon number 7 (see example).

## num-eigenvalues

Request number of eigenvalues (excitation energies).

**Input line****Default**

```
num-eigenvalues:
[integer]
```

`num-eigenvalues: 4`

**Example**

`num-eigenvalues: 10`

## convergence

Convergence threshold for excitation energies in [a.u.].

**Input line****Default**

```
convergence:
[real]
```

`convergence: 1.0e-3`

**Example**

`convergence: 1.0e-4`

## maxdim-subspace

Specify the maximum dimension of the reduced subspace into which the true TDDFT operator is projected.

**Input line****Default**

```
maxdim-subspace:
[integer]
```

`maxdim-subspace: 80`

**Example**

`maxdim-subspace: 300`

## tamm-dancoff-approximation

Use Tamm-Dancoff approximation.

**Input line****Default**

```
tamm-dancoff-approximation:
[Boolean]
```

`tamm-dancoff-approximation: False`

**Example**

`tamm-dancoff-approximation: True`

## pe-rotations

Include positive-energy-state/negative-energy-state rotations in the calculation.

**Input line****Default**

```
pe-rotations:
[Boolean]
```

`pe-rotations: False`

**Example**

`pe-rotations: True`

## Latest Publications

### Book chapter on relativistic real-time electron dynamics

### Book chapter on relativistic theory of EPR and (p)NMR

## Useful Links

## Our Contacts

Department of Chemistry

UiT The Arctic University of Norway

Tromsø, NO-9037 Norway

Email: info@respectprogram.eu