(calculator_interfaces)=

# Interfaces to calculators

The interfaces for VASP, WIEN2k, Quantum ESPRESSO (QE), ABINIT, Elk, SIESTA,
CRYSTAL, DFTB+, TURBOMOLE, FHI-AIMS, CASTEP, ABACUS, and LAMMPS are built in to
the usual phonopy command. See the command options and how to invoke each of
them at {ref}`force_calculators`. {ref}`LAMMPS interface
<external_tools_phonolammps>` is provided as an external tool by Abel Carreras.

(interfaces_to_force_calculators)=

## List of force calculators

Short tutorials for the force calculators are found in the following pages.

```{toctree}
:maxdepth: 1
vasp
wien2k
qe
abinit
siesta
elk
crystal
dftb+
turbomole
cp2k
aims
castep
Fleur
abacus
lammps
```

The VASP DFPT interface reads `vasprun.xml` and creates `FORCE_CONSTANTS` file.

```{toctree}
:maxdepth: 1
vasp-dfpt
```

(interfaces-physical-units)=
## Physical unit system for calculator

Physical unit systems used for the calculators are as follows:

```
          | Distance   Atomic mass   Force         Force constants
-----------------------------------------------------------------
VASP      | Angstrom   AMU           eV/Angstrom   eV/Angstrom^2
WIEN2k    | au (bohr)  AMU           mRy/au        mRy/au^2
QE        | au (bohr)  AMU           Ry/au         Ry/au^2
ABINIT    | au (bohr)  AMU           eV/Angstrom   eV/Angstrom.au
SIESTA    | au (bohr)  AMU           eV/Angstrom   eV/Angstrom.au
Elk       | au (bohr)  AMU           hartree/au    hartree/au^2
CRYSTAL   | Angstrom   AMU           eV/Angstrom   eV/Angstrom^2
TURBOMOLE | au (bohr)  AMU           hartree/au    hartree/au^2
CP2K      | Angstrom   AMU           hartree/au    hartree/Angstrom.au
FHI-AIMS  | Angstrom   AMU           eV/Angstrom   eV/Angstrom^2
Fleur     | au (bohr)  AMU           hartree/au    hartree/au^2
CASTEP    | Angstrom   AMU           eV/angstrom   eV/angstrom^2
ABACUS    | au (bohr)  AMU           eV/angstrom   eV/angstrom.au
LAMMPS    | Angstrom   AMU           eV/Angstrom   eV/Angstrom^2
```

For these sets of physical properties, phonon frequency is calculated in THz.

## Default file name, value, and conversion factor

### Default unit cell file name for calculator

Without specifying `-c` option, default file names of unit cell shown below is
searched in current directory. When generating supercells with `-c` option,
the default supercell file names based on those shown below are used.

```
VASP      | POSCAR        | SPOSCAR
WIEN2k    | case.struct   | case.structS
QE        | unitcell.in   | supercell.in
ABINIT    | unitcell.in   | supercell.in
SIESTA    | input.fdf     | supercell.fdf
Elk       | elk.in        | supercell.in
CRYSTAL   | crystal.o     | -
DFTB+     | geo.gen       | geo.genS
TURBOMOLE | control       | -
CP2K      | unitcell.inp  | -
FHI-AIMS  | geometry.in   | geometry.in.supercell
Fleur     | fleur.in      | supercell.in
CASTEP    | unitcell.cell | supercell.cell
ABACUS    | STRU          | STRU.in
LAMMPS    | unitcell      | supercell
```

### Default displacement distances

Without specifying `DISPLACEMENT_DISTANCE` tag or `--amplitude` option, default
displacement distance is used when creating supercells with displacements
`CREATE_DISPLACEMENTS = .TRUE.` or `-d` option. The default value is dependent
on calculator, and the list is shown below:

```
VASP      | 0.01 Angstrom
WIEN2k    | 0.02 au (bohr)
QE        | 0.02 au (bohr)
ABINIT    | 0.02 au (bohr)
SIESTA    | 0.02 au (bohr)
Elk       | 0.02 au (bohr)
CRYSTAL   | 0.01 Angstrom
DFTB+     | 0.01 au (bohr)
TURBOMOLE | 0.02 au (bohr)
CP2K      | 0.01 Angstrom
FHI-AIMS  | 0.01 Angstrom
Fleur     | 0.02 au (bohr)
CASTEP    | 0.01 Angstrom
ABACUS    | 0.02 au (bohr)
LAMMPS    | 0.01 Angstrom
```

(frequency_default_value_interfaces)=

### Default unit conversion factor of phonon frequency to THz

```
VASP      | 15.633302
WIEN2k    | 3.44595837
QE        | 108.97077
ABINIT    | 21.49068
SIESTA    | 21.49068
Elk       | 154.10794
CRYSTAL   | 15.633302
DFTB+     | 154.10794
TURBOMOLE | 154.10794
CP2K      | 112.10516
FHI-AIMS  | 15.633302
Fleur     | 154.10794
CASTEP    | 15.633302
ABACUS    | 21.49068
LAMMPS    | 15.633302
```

(nac_default_value_interfaces)=

### Default unit conversion factor for non-analytical term correction

```
VASP      | 14.399652
WIEN2k    | 2000
QE        | 2
ABINIT    | 51.422090
SIESTA    | 51.422090
Elk       | 1
CRYSTAL   | 14.399652
DFTB+     | 14.399652
TURBOMOLE | 1
CP2K      | None (N/A)
FHI-AIMS  | 14.399652
Fleur     | 1 (but feature N/A)
CASTEP    | 14.399652
ABACUS    | 51.422090
LAMMPS    | 14.399652
```