ASE Support

ASE calculator implementation for the dftd4 program.

This module provides a basic single point calculator implementations to integrate the dftd4 API into existing ASE workflows. To use DFTD4 as dispersion correction the ase.calculators.mixing module can be used to combine DFTD4 with a DFT calculator using the SumCalculator.

Supported properties by this calculator are:

• energy (free_energy)

• forces

• stress

Supported keywords are

Keyword	Default	Description
method	None	Method to calculate dispersion for
params_tweaks	None	Optional dict with the damping parameters
cache_api	True	Reuse generate API objects (recommended)
model	d4	Used dispersion Model (D4S or D4 (default))
realspace_cutoff	None	Optional realspace cutoff settings

Example

>>> from ase.build import molecule
>>> from dftd4.ase import DFTD4
>>> atoms = molecule('H2O')
>>> atoms.calc = DFTD4(method="TPSS")
>>> atoms.get_potential_energy()
-0.007310393443152083
>>> atoms.calc.set(method="PBE")
{'method': 'PBE'}
>>> atoms.get_potential_energy()
-0.005358475432239303
>>> atoms.get_forces()
array([[-0.        , -0.        ,  0.00296845],
       [-0.        ,  0.00119152, -0.00148423],
       [-0.        , -0.00119152, -0.00148423]])

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	16.0	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!

Example

>>> from dftd4.ase import DFTD4
>>> calc = DFTD4(params_tweaks={"s8": 0.5, "a1": 0.4, "a2": 4.0})
>>> calc.set(params_tweaks={"s8": 0.6, "a1": 0.5, "a2": 3.0})
{'params_tweaks': {'s8': 0.6, 'a1': 0.5, 'a2': 3.0}}
>>> calc.set(params_tweaks={}, method="TPSS")
{'params_tweaks': {}, 'method': 'TPSS'}

The realspace_cutoff option defines all cutoff values used for computing realspace summations.

Name	Default	Description
disp2	60.0 * Bohr	Cutoff for the pairwise dispersion energy
disp3	40.0 * Bohr	Cutoff for the three-body dispersion energy
cn	30.0 * Bohr	Cutoff for the coordination number calculation
width2	0.0	Smooth cutoff width for the pairwise dispersion
width3	0.0	Smooth cutoff width for the three-body dispersion

The realspace_cutoff dict can contain disp2, disp3, and cn cutoffs, as well as smooth cutoff widths width2 and width3. Values are expected in Angstrom. To set values in Bohr, e.g. to match the default values, use the ASE units module for converting them. By multiplying with Bohr the values are converted to Angstrom. An empty dict will reset the cutoff values to the library defaults. The smooth cutoff widths are optional but highly recommended to avoid discontinuities especially for small cutoff values or periodic systems (recommended are 0.05 Bohr).

Example

>>> from ase.units import Bohr
>>> from dftd4.ase import DFTD4
>>> calc = DFTD4(method="TPSS")
>>> calc.set(realspace_cutoff={"width2": 0.05 * Bohr, "width3": 0.05 * Bohr})
{'realspace_cutoff': {'width2': 0.02645886052819206, 'width3': 0.02645886052819206}}
>>> calc.set(realspace_cutoff={})  # reset to library defaults
{'realspace_cutoff': {}}

class dftd4.ase.DFTD4(atoms=None, **kwargs)

ASE calculator for DFT-D4 related methods. The DFTD4 class can access all methods exposed by the dftd4 API.

Example

>>> from ase.build import molecule
>>> from ase.calculators.mixing import SumCalculator
>>> from ase.calculators.nwchem import NWChem
>>> from dftd4.ase import DFTD4
>>> atoms = molecule('H2O')
>>> atoms.calc = SumCalculator([DFTD4(method="PBE"), NWChem(xc="PBE")])

add_calculator(other)

Convenience function to allow DFTD4 to combine itself with another calculator by returning a SumCalculator:

Example

>>> from ase.build import molecule
>>> from ase.calculators.emt import EMT
>>> from dftd4.ase import DFTD4
>>> atoms = molecule("C60")
>>> atoms.calc = DFTD4(method="pbe").add_calculator(EMT())
>>> atoms.get_potential_energy()
6.348142387048062
>>> [calc.get_potential_energy() for calc in atoms.calc.calcs]
[-6.015477436263984, 12.363619823312046]

calculate(atoms=None, properties=None, system_changes=['positions', 'numbers', 'cell', 'pbc', 'initial_charges', 'initial_magmoms'])

Perform actual calculation with by calling the dftd4 API

default_parameters = {'cache_api': True, 'method': None, 'model': 'd4', 'params_tweaks': {}, 'realspace_cutoff': {}}

Default parameters

implemented_properties = ['energy', 'forces', 'stress']

Properties calculator can handle (energy, forces, …)

reset()

Clear all information from old calculation

set(**kwargs)

Set new parameters to dftd4