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asedftk documentation

asedftk is a wrapper around the density-functional toolkit (DFTK), a Julia code for plane-wave based density-functional theory (PWDFT). asedftk provides an ASE-compatible calculator class, which allows to directly employ DFTK inside ASE workflows.

Installation

  1. Install Julia e.g. by downloading the binary. The use of at least Julia 1.5 is required.
  2. Install asedftk from PyPi, for example using pip: 
    pip install asedftk
    Note: You can also use pip if you are managing your python packages with anaconda (conda install pip followed by above command), but it is not recommended to do this in the root anaconda environment.

This will automatically install DFTK inside a separate Julia environment private to asedftk. Typically this DFTK version will be updated as needed. In case you need to do the update manually at some point, simply run asedftk.update().

Some examples

The best way to explain asedftk is by some examples:

Silicon energy and forces

from asedftk import DFTK
import ase.build

silicon = ase.build.bulk("Si")
silicon.calc = DFTK()

print("Silicon energy: ", silicon.get_potential_energy())
print("Silicon forces: ", silicon.get_forces())

Magnesium energy and forces

from asedftk import DFTK
import ase.build

magnesium = ase.build.bulk("Mg")
magnesium.calc = DFTK(xc="PBE", smearing=("Gaussian", 0.027), kpts=(5, 5, 5))
print("Magnesium energy: ", magnesium.get_potential_energy())
print("Magnesium forces: ", magnesium.get_forces())

Hydrogen geometry optimisation

Using the ASE optimiser from python:

# Python
from asedftk import DFTK
import ase.build
from ase.optimize import BFGS

h2 = ase.build.molecule("H2", pbc=True, vacuum=10)
h2.set_positions([[10, 10, 11.0], [10, 10, 10]])
h2.calc = DFTK(scftol=1e-6, xc="PBE", kpts=[1, 1, 1], ecut=50)

dyn = BFGS(h2, trajectory="H2.traj")
dyn.run(fmax=0.05)

print("H-H distance: ", h2.get_distance(0, 1))

Alternatively using a Julia script (and PyCall) to drive the optimisation:

# Julia
using PyCall
DFTKcalc = pyimport("asedftk").DFTK
ase_build = pyimport("ase.build")
BFGS = pyimport("ase.optimize").BFGS

h2 = ase_build.molecule("H2", pbc=true, vacuum=10)
h2.set_positions([[10 10 11.0]; [10 10 10]])
h2.calc = DFTKcalc(scftol=1e-6, xc="PBE", kpts=[1, 1, 1], ecut=50)

dyn = BFGS(h2, trajectory="H2.traj")
dyn.run(fmax=0.05)

println("H-H distance: ", h2.get_distance(0, 1))

DFTK parameters

The asedftk.DFTK class supports a couple of parameters to customise the calculation, mostly following the ASE calculator interface proposal. See also the __init__ function in calculator.jl.

  • ecut: Kinetic energy cutoff. 400eV by default.
  • functionals: Explicit functional list. This overwrites the choice of xc, but xc still needs to be given to select appropriate pseudopotentials. Valid options are all functionals from libxc, for example "lda_x", "GGA_X_B86", "GGA_C_LYP".
  • kpts: k-point grid to use. Valid options are:
    • (n1,n2,n3): (Unshifted) Monkhorst-Pack grid
    • (n1,n2,n3,"gamma"): Shifted MP grid to contain the gamma point.
    • [(k11,k12,k13),(k21,k22,k23),...]: Explicit k-Point list in units of the reciprocal lattice vectors
    • 3.5 (or any float): k-point density as in 3.5 kpoints per Ǎngström.
  • mixing: Mixing scheme used during SCF iterations. Examples for valid options:
    • "SimpleMixing(α=0.7)": Simple mixing with damping 0.7
    • "KerkerMixing(α=0.7, kTF=1.0)": Kerker mixing with damping α = 0.7 and screening parameter kTF = 1.0. Applies the operator kernel α * G^2 / (kTF^2 + G^2) for a wave vector G in frequency space.
    • "HybridMixing(α=0.7, kTF=1.0, εr=10)": LDOS mixing as described in arXiv 2009.01665. If εr=1 a plain LDOS mixing is used, for other values a model dielectric term is added as well. kTF is meaningless unless the model dielectric term is used.
  • nbands: Number of bands to compute
  • pps: Pseudopotential family. Currently the only choices are "hgh" (Goedecker-type pseudos) and "hgh.k" (semi-core version of "hgh").
  • scftol: Convergence tolerance of the SCF. Default 1e-5.
  • smearing: Smearing function and temperature, options:
    • ('Fermi-Dirac', width)
    • ('Gaussian', width)
    • ('Methfessel-Paxton', width, n) where in each case width is the width in eV and n is the Methfessel-Paxton order.
  • xc: Exchange-correlation functional, default is LDA, options are LDA or PBE.
  • n_mpi: Number of MPI threads to employ when running DFTK. Set this to a value between 1 and the number of irreducible k-Points. See the DFTK parallelization documentation for details.
  • n_threads: Number of Julia threads to employ when running DFTK. Typically the best setting is to use only one thread (the default). See the DFTK parallelization documentation for details.

Custom Julia environment for asedftk

If you want to employ a custom Julia environment in combination with asedftk, for example to supply a modified DFTK, just point the environment variable ASEDFTK_DFTK_ENVIRONMENT to the folder with your custom environment. When doing this, ensure that the packages specified in asedftk's Project.toml are available in your custom environment.