## field

## mowindow

Enable the selective perturbation (SP) approach. By this, only certain molecular orbitals are perturbed by an applied external field.

**Input block**

**Extended variant**

`mowindow:`

`occupied: [intial-mo-index] - [final-mo-index]`

`virtual: [intial-mo-index] - [final-mo-index]`

**Default**

`none`

**Example**

```
mowindow:
occupied: 4-6
```

```
mowindow:
occupied: 7-10
virtual: 15-46
```

### Note

- By default, entire orbital spectrum is affected by the perturbation.

- Occupied and virtual orbitals must be within their respective range. The range for occupied orbitals is from 1 to HOMO, whereas the range for virtual orbitals is from HOMO+1 to the total number of MOs.

### Tip

- SP turns out to be particularly useful for X-ray spectroscopies, where excitations occur only from specific core-shell orbitals. Here, we recommed to select for perturbation only the core-shell occupied MOs.

## analysis

Enable the transition density matrix analysis (TDMA). By this, information about particular occupied-virtual MO-pairs involved in spectral transitions can be determined.

**Input block**

**Extended variant**

`analysis:`

`occupied: [intial-mo-index] - [final-mo-index]`

`virtual: [intial-mo-index] - [final-mo-index]`

`threshold: [real]`

**Default**

`none`

**Example**

```
analysis:
occupied: 8-10
virtual: 11-25
threshold: 1.0e-5
```

### Note

- By default, TDMA is disabled.

- Occupied and virtual orbitals must be within their respective range. The range for occupied orbitals is from 1 to HOMO, whereas the range for virtual orbitals is from HOMO+1 to the total number of MOs.

### Tip

- Since TDMA may lead to an extensive data printout, we recommend to select only those orbitals relevant for the spectroscopy of interest.

## spectroscopy

## time-steps

Define the time propagation details.

**Input line****Default**

```
time-steps:
[number-time-steps] x [time-step-length]
```

`none`

**Example**

`time-steps: 5000 x 0.05`

## solver

## maxiterations

Define the maximum number of micro-iterations (per time step) for the Magnus solver.

**Input line****Default**

```
maxiterations:
[integer]
```

`maxiterations: 8`

**Example**

`maxiterations: 5`

### Warning

- This keyword is relevant only for the Magnus solver, i.e. if "solver:magnus" is used.

## convergence

Define the convergence threshold for the Magnus solver.

**Input line****Default**

```
convergence:
[real]
```

`convergence: 1.0e-07`

**Example**

`convergence: 1.0e-5`

### Warning

- This keyword is relevant only for the Magnus solver, i.e. if "solver:magnus" is used.

## checkpoint

Define the frequency of data checkpointing during the time propagation.

**Input line****Default**

```
checkpoint:
[integer]
```

`checkpoint: 100`

**Example**

`checkpoint: 500`

## x2c-transformation

Specify if one-electron operators are X2C picture-change transformed.

**Input line****Default**

```
x2c-transformation:
[string]
```

`x2c-transformation: on`

**Example**

`x2c-transformation: off`

### Warning

- This keyword is relevant only for the X2C-type Hamiltonians.

## Latest Publications

### pNMR study of Ru(III) systems

### General trends of NMR SO-HALA effects explained

## Useful Links

## Our Contacts

UiT The Arctic University of Norway

Tromsø, NO-9037 Norway

Email: info@respectprogram.eu