Adding new calculators

Adding an ASE interface to your favorite force-calculator is very simple. Take a look at the Calculator and FileIOCalculator classes below (the code is here: ase/calculators/ You should inherit from the FileIOCalculator and implement the read(), read_results() and write_input() methods. The methods set(), check_state() and set_label() may also need to be implemented.

See also

Description of base-classes

The Calculator base-class

class ase.calculators.calculator.Calculator(restart=None, ignore_bad_restart_file=False, label=None, atoms=None, **kwargs)[source]

Base-class for all ASE calculators.

A calculator must raise PropertyNotImplementedError if asked for a property that it can’t calculate. So, if calculation of the stress tensor has not been implemented, get_stress(atoms) should raise PropertyNotImplementedError. This can be achieved simply by not including the string ‘stress’ in the list implemented_properties which is a class member. These are the names of the standard properties: ‘energy’, ‘forces’, ‘stress’, ‘dipole’, ‘charges’, ‘magmom’ and ‘magmoms’.

Basic calculator implementation.

restart: str
Prefix for restart file. May contain a directory. Default is None: don’t restart.
ignore_bad_restart_file: bool
Ignore broken or missing restart file. By default, it is an error if the restart file is missing or broken.
label: str
Name used for all files. May contain a directory.
atoms: Atoms object
Optional Atoms object to which the calculator will be attached. When restarting, atoms will get its positions and unit-cell updated from file.
implemented_properties = []

Properties calculator can handle (energy, forces, …)

default_parameters = {}

Default parameters


Set label and convert label to directory and prefix.


  • label=’abc’: (directory=’.’, prefix=’abc’)
  • label=’dir1/abc’: (directory=’dir1’, prefix=’abc’)

Calculators that must write results to files with fixed names can overwrite this method so that the directory is set to all of label.


Clear all information from old calculation.


Read atoms, parameters and calculated properties from output file.

Read result from self.label file. Raise ReadError if the file is not there. If the file is corrupted or contains an error message from the calculation, a ReadError should also be raised. In case of succes, these attributes must set:

atoms: Atoms object
The state of the atoms from last calculation.
parameters: Parameters object
The parameter dictionary.
results: dict
Calculated properties like energy and forces.

The method will typically read atoms and parameters and get the results dict by calling the read_results() method.


Set parameters like set(key1=value1, key2=value2, …).

A dictionary containing the parameters that have been changed is returned.

Subclasses must implement a set() method that will look at the chaneged parameters and decide if a call to reset() is needed. If the changed parameters are harmless, like a change in verbosity, then there is no need to call reset().

The special keyword ‘parameters’ can be used to read parameters from a file.

check_state(atoms, tol=1e-15)[source]

Check for system changes since last calculation.


Calculate magnetic moments projected onto atoms.

calculate(atoms=None, properties=[‘energy’], system_changes=[‘positions’, ‘numbers’, ‘cell’, ‘pbc’, ‘initial_charges’, ‘initial_magmoms’])[source]

Do the calculation.

properties: list of str
List of what needs to be calculated. Can be any combination of ‘energy’, ‘forces’, ‘stress’, ‘dipole’, ‘charges’, ‘magmom’ and ‘magmoms’.
system_changes: list of str
List of what has changed since last calculation. Can be any combination of these six: ‘positions’, ‘numbers’, ‘cell’, ‘pbc’, ‘initial_charges’ and ‘initial_magmoms’.

Subclasses need to implement this, but can ignore properties and system_changes if they want. Calculated properties should be inserted into results dictionary like shown in this dummy example:

self.results = {'energy': 0.0,
                'forces': np.zeros((len(atoms), 3)),
                'stress': np.zeros(6),
                'dipole': np.zeros(3),
                'charges': np.zeros(len(atoms)),
                'magmom': 0.0,
                'magmoms': np.zeros(len(atoms))}

The subclass implementation should first call this implementation to set the atoms attribute.

calculate_numerical_forces(atoms, d=0.001)[source]

Calculate numerical forces using finite difference.

All atoms will be displaced by +d and -d in all directions.

calculate_numerical_stress(atoms, d=1e-06, voigt=True)[source]

Calculate numerical stress using finite difference.


Create band-structure object for plotting.

The FileIOCalculator class

class ase.calculators.calculator.FileIOCalculator(restart=None, ignore_bad_restart_file=False, label=None, atoms=None, command=None, **kwargs)[source]

Base class for calculators that write/read input/output files.

File-IO calculator.

command: str
Command used to start calculation.
command = None

Command used to start calculation

write_input(atoms, properties=None, system_changes=None)[source]

Write input file(s).

Call this method first in subclasses so that directories are created automatically.


Read energy, forces, … from output file(s).