How to use Fireball

Fireball as an ase.calculators.calculator.Calculator needs to be attached first to a valid ase.Atoms object. This may be done by setting the calc attribute:

>>> from ase.build import molecule
>>> from fireballpy import Fireball
>>> atoms = molecule('CH4')
>>> atoms.calc = Fireball(fdata='biology')

Do not worry about the fdata argument. Its importance will become clear later. We are now ready to perform some computations! Let’s get the energy, charges and forces:

>>> atoms.get_potential_energy()
-216.68505107072147
>>> atoms.get_charges()
array([-0.44507143,  0.11126785,  0.11126785,  0.11126786,  0.11126786])
>>> atoms.get_forces()
array([[ 1.73489876e-15,  5.49377383e-15, -1.99149954e-07],
...    [-2.81616200e-01, -2.81616200e-01, -2.81616191e-01],
...    [ 2.81616200e-01,  2.81616200e-01, -2.81616191e-01],
...    [-2.81616282e-01,  2.81616282e-01,  2.81616290e-01],
...    [ 2.81616282e-01, -2.81616282e-01,  2.81616290e-01]])

Nice! We got our first results for a methane molecule.

Now, if this is the first time you run this tutorial you may have noticed what appeared to be a download before any computation took place. This is because we requiere the precomputed integrals of our base functions. How we select which basis we desire? Well that’s were the fdata argument comes into play!

In the next section we will discuss a bit more about FData and their crucial role.