ASE Support

ASE calculator implementation for the s-dftd3 program.

This module provides a basic single point calculator implementations to integrate the s-dftd3 API into existing ASE workflows. To use DFTD3 as dispersion correction the ase.calculators.mixing module can be used to combine DFTD3 with a DFT calculator using the SumCalculator.

Supported properties by this calculator are:

• energy (free_energy)

• forces

• stress

• hessian

The hessian is not a standard ASE property, it is provided as a 3*nat by 3*nat matrix in eV per Angstrom squared and can be requested with atoms.calc.get_hessian(atoms).

Supported keywords are

Keyword	Default	Description
method	None	Method to calculate dispersion for
damping	None	Damping function to use
params_tweaks	{}	Optional dict with the damping parameters
realspace_cutoff	{}	Optional dict to override cutoff values
ewald	None	Optional dict to enable the Ewald summation
ghost_atoms	None	Disable dispersion contributions from these atoms
cache_api	True	Reuse generate API objects (recommended)

The ewald dict enables the reciprocal space summation of the two-body dispersion energy, which removes the truncation error of the real space summation. An empty dict selects the default settings, the entries rank, tolerance and kcut allow to control the accuracy. The mesh entry switches to the particle mesh evaluation, which is substantially faster for large cells. Requires three-dimensional periodic boundary conditions and either the rational or the zero damping function.

The params_tweaks dict contains the damping parameters, at least s8, a1 and a2 must be provided

Tweakable parameter	Default	Description
s6	1.0	Scaling of the dipole-dipole dispersion
s8	None	Scaling of the dipole-quadrupole dispersion
s9	1.0	Scaling of the three-body dispersion energy
a1	None	Scaling of the critical radii
a2	None	Offset of the critical radii
alp	14.0	Exponent of the zero damping (ATM only)

Either method or s8, a1 and a2 must be provided, s9 can be used to overwrite the ATM scaling if the method is provided in the model. Disabling the three-body dispersion (s9=0.0) changes the internal selection rules for damping parameters of a given method and prefers special two-body only damping parameters if available!

The realspace cutoff parameters allow adjusting the distance values for which interactions are considered

Realspace cutoff	Default	Description
disp2	60 * Bohr	Pairwise dispersion interactions
disp3	40 * Bohr	Triple dispersion interactions
cn	40 * Bohr	Coordination number counting
width2	0 * Bohr	Smooth cutoff width for pairwise dispersion
width3	0 * Bohr	Smooth cutoff width for triple dispersion

Values provided in the dict are expected to be in Angstrom. When providing values in Bohr multiply the inputs by the ase.units.Bohr constant.

Example

>>> from ase.build import molecule
>>> from dftd3.ase import DFTD3
>>> atoms = molecule('H2O')
>>> atoms.calc = DFTD3(method="TPSS", damping="d3bj")
>>> atoms.get_potential_energy()
-0.011441640787279111
>>> atoms.calc.set(method="PBE")
{'method': 'PBE'}
>>> atoms.get_potential_energy()
-0.009781920198843976
>>> atoms.get_forces()
array([[-0.        , -0.        ,  0.00009572],
       [-0.        , -0.00004060, -0.00004786],
       [-0.        ,  0.00004060, -0.00004786]])