Jacapo - ASE python interface for Dacapo


Jacapo is an ASE interface for Dacapo that is fully compatible with ASE. It replaces the old Dacapo interface using Numeric python and ASE2. The code was originally developed by John Kitchin and detailed documentation as well as many examples are available online:


Jacapo is included as an optional calculator in ASE and small differences to the above documentation may occur, and the documentation is no longer maintained.

Jacapo calculator

The Jacapo interface is automatically installed with ase and can be imported using:

from ase.calculators.jacapo import Jacapo

(You will need to have a working installation of Dacapo, however.)

class ase.calculators.jacapo.Jacapo

Here is a list of available keywords to initialize the calculator:

keyword type description
nc str Output NetCDF file, or input file if nc already exists.
outnc str Output file. By default equal to nc.
atoms object Atoms object
pw float Planewave cutoff in eV
dw float Density cutoff in eV
xc str Exchange-correlation functional. One of [‘PZ’,’VWN’,’PW91’,’PBE’,’RPBE’,’revPBE’]
nbands int Number of bands
ft float Fermi temperature
kpts list K-point grid, e.g. kpts = (2,2,1)
spinpol boolean Turn on/off spin-polarization
fixmagmom str Magnetic moment of the unit cell
symmetry boolean Turn on/off symmetry reduction
stress boolean Turn on/off stress calculation
dipole boolean Turn on/off dipole correction
ados dict Atom-projected density of states
stay_alive boolean Turn on/off stay alive
debug int Set debug level (0=off, 10=extreme)
deletenc boolean If the nc file exists, delete it (to ensure a fresh run). Default is False.


Here is an example of how to calculate the total energy of a H atom.


This is an example only - the parameters are not physically meaningful!

from ase import Atoms, Atom
from ase.io import write
from ase.calculators.jacapo import Jacapo

atoms = Atoms([Atom('H',[0,0,0])],

calc = Jacapo('Jacapo-test.nc',


write('Jacapo-test.traj', atoms)

Note that all calculator parameters should be set in the calculator definition itself. Do not attempt to use the calc.set_* commands as they are intended to be internal to the calculator. Note also that Dacapo can only operate with periodic boundary conditions, so be sure that pbc is set to True.

Restarting from an old calculation

If the file you specify to Jacapo with the nc keyword exists, Jacapo will assume you are attempting to restart an existing calculation. If you do not want this behavior, turn the flag deletenc to True in your calculator definition.

For example, it is possible to continue a geometry optimization with something like this:

calc = Jacapo('old.nc', stay_alive=True)
atoms = calc.get_atoms()
dyn = QuasiNewton(atoms, logfile='qn.log')

Note, that the stay_alive flag is not stored in the .nc file and must be set when the calculator instance is created.

Atom-projected density of states

To find the atom-projected density of states with Jacapo, first specify the ados dictionary in your calculator definition, as in:

calc = Jacapo( ... ,
              ados={'energywindow': (-10., 5.),
                    'energywidth': 0.2,
                    'npoints': 250,
                    'cutoff': 1.0})

After this is established, you can use the get_ados command to get the desired ADOS data. For example:

energies, dos = calc.get_ados(atoms=[0],