## method

Specify the type of molecular Hamiltonian for SCF (and subsequent property) calculations.

**Input block**

**Short variant**

```
method:
[hamiltonian]
/
[functional]
```

**Extended variant**

`method:`

`hfx: [integer]`

`functional: [functional]`

`hamiltonian: [hamiltonian]`

**Default**

`none`

**Example**

`method: hf`

`method: ks-1eX2C/b3lyp`

```
method:
hamiltonian: ks-1eX2C
functional: b3lyp
hfx: 40
```

### Note

- The explicit definition of [functional] is mandatory for all [hamiltonian]s of the Kohn–Sham type.

## geometry

Specify the molecular geometry.

**Input block**

**Extended variant**

`geometry:`

`[element-symbol] [x] [y] [z]`

**Default**

`none`

**Example**

```
#water in the xyz format
geometry:
H -0.756690 +0.466877 0.000000
H +0.756690 +0.466877 0.000000
O +0.000000 -0.119015 0.000000
```

```
#ethylene in the z-matrix format
geometry:
H
C 1 1.08
H 2 1.08 1 120.0
C 2 1.40 3 120.0 1 180.0
H 4 1.08 2 120.0 1 180.0
H 4 1.08 2 120.0 1 0.000
```

### Note

- Angstroms are used as default units for geometry.

- The geometry can be provided either in the Cartesian (xyz) format or in the Z-matrix format.

### Tip

- The default units can be changed by the keyword "geo-units".

## basis

Specify atomic orbital basis sets.

**Input block**

**Short variant**

```
basis:
[basis-name]
```

**Extended variant**

`basis:`

`all : [basis-name]`

`[element-index] : [basis-name]`

`[element-symbol]: [basis-name]`

**Default**

`none`

**Example**

In this example, the orbital basis "ucc-pvdz" is assigned to all elements.

`basis: ucc-pvdz`

In this example, the orbital basis "upc-1" is assigned first to all elements. Then, the basis is replaced by "ucc-pvdz" for the 4th element (as specified in the input block "geometry") and "dyall-vdz" for all bromine atoms.

```
basis:
all : upc-1
4 : ucc-pvdz
Br : dyall-vdz
```

### Note

- In relativistic calculations the orbital basis must be in an uncontracted form. All basis sets from the internal program library are of this form.

### Tip

- The complete list of available [basis-name]s can be found here.

## auxbas

Specify atomic auxiliary basis sets.

**Input block**

**Short variant**

```
auxbas:
[basis-name]
```

**Extended variant**

`auxbas:`

`all : [basis-name]`

`[element-index] : [basis-name]`

`[element-symbol]: [basis-name]`

**Default**

`none`

**Example**

In this example, the auxiliary basis "ucc-pvtz" is assigned to all elements.

`auxbas: ucc-pvtz`

In this example, the auxiliary basis "upc-1" is assigned first to all elements. Then, the basis is replaced by "ucc-pvdz" for the 4th element (as specified in the input block "geometry") and "dyall-vdz" for all bromine atoms.

```
auxbas:
all : upc-1
4 : ucc-pvdz
Br : dyall-vdz
```

### Note

- The use of auxiliary basis makes sense only in connection with an approximative evaluation of electron repulsion integrals (ERI) by means of the resolution-of-identity (RI) technique. This is controled by the keyword "acceleration" in the "eri" block.

- The names of matching orbital and auxiliary basis sets are identical. Therefore, one can omit the definition of auxiliary basis, provided the orbital basis was selected from the internal program library. In this case, the program will assign the auxiliary basis automatically.

## 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-type]
```

**Extended variant**

`grid:`

`[element-index]: [grid-type]`

`[element-symbol]: [grid-type]`

**Default**

```
grid: medium
```

**Example**

`grid: large`

```
grid:
C: medium
5: coarse
```

## pcm

Specify the polarizable continuum solvent model for SCF (and subsequent property) calculations.

## charge

Specify the total molecular charge.

**Input line****Default**

```
charge:
[integer]
```

`charge: 0`

**Example**

`charge: -2`

## multiplicity

Specify the spin multiplicity.

**Input line****Default**

```
multiplicity:
[integer]
```

`multiplicity: 1 #singlet`

**Example**

`multiplicity: 3 #triplet`

## convergence

Specify the convergence threshold for SCF iterations.

**Input line****Default**

```
convergence:
[real]
```

`convergence: 1.0e-06`

**Example**

`convergence: 2.5e-5`

### Tip

- We recommend to set the threshold value to ~1.0e-4 in cases when a loose SCF convergence is sufficient, such as in initial guess calculations, etc. For productive runs, however, the thresholds setup within the range 1.0e-5—1.0e-6 is advised. Tight convergence in the SCF is considered for thresholds below 1.0e-7.

## maxiterations

Specify the maximum number of SCF iterations.

**Input line****Default**

```
maxiterations:
[integer]
```

`maxiterations: 30`

**Example**

`maxiterations: 25`

## nc-model

Specify the nuclear charge distribution model.

## cscale

Scale the speed of light by a factor.

**Input line****Default**

```
cscale:
[real]
```

`cscale: 1.0`

**Example**

`cscale: 20.0`

### Note

- The scaling factor should be a positive real number. By setting cscale < 1.0, the speed of light decreases and molecular systems turn into a hyper-relativistic regime where all relativistic terms become amplified. On the other hand, by setting cscale > 1.0 the speed of light increases and molecular systems approach their non-relativistic limit.

### Warning

- Due to numerical reasons, the users are advised to set the cscale parameter within the limits: 0.1 < cscale < 50.0.

## soscale

Scale the spin-orbit operators by a factor.

**Input line****Default**

```
soscale:
[real]
```

`soscale: 1.0`

**Example**

`soscale: 0.0`

### Note

- The scaling factor should be a positive real number. By setting soscale = 0.0, one can switch off the spin-orbit interaction completely.

### Warning

- Due to numerical reasons, the users are advised to set the soscale parameter within the limits: 0.0 < soscale < 1.0.

## checkpoint

Specify the frequency of data checkpointing during SCF iterations.

**Input line****Default**

```
checkpoint:
[integer]
```

`checkpoint: 10`

**Example**

`checkpoint: 2`

### Tip

- The importance of more frequent checkpointing -- storing intermediate SCF data to disk for the later reuse as a restart -- increases with the system size.

## spin

Control the initial orientation of spin polarization in relativistic SCF calculations.

**Input line****Default**

```
spin:
[string]
```

`spin: z`

**Example**

`spin: x`

### Note

- This keyword plays an important role only in relativistic Kramers-unrestricted calculations of open-shell molecules, in particular in connections with the EPR property calculations, as it controls the initial orientation of the spin polarization. In non-relativistic regime, however, the keyword does not make a sense and is therefore ignored.

## spinfix

Impose a spin fixation procedure in relativistic SCF calculations of open-shell molecules.

**Input line****Default**

```
spinfix:
[string]
```

`spinfix: off`

**Example**

`spinfix: on`

### Note

- This keyword plays an important role only in relativistic Kramers-unrestricted calculations of open-shell molecules, in particular in connections with the EPR property calculations, as it enforces the orientation of the spin polarization during SCF iterations. In non-relativistic regime, however, the keyword does not make a sense and is therefore ignored.

## Latest Publications

### Analysis and visualization of NMR spin-spin coupling constants

### ReSpect reference paper just published in J.Chem.Phys.

## Useful Links

## Our Contacts

Department of Chemistry

UiT The Arctic University of Norway

Tromsø, NO-9037 Norway

Email: info@respectprogram.eu