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Usage in DFTB+

Usage in DFTB+#

The tblite project started as an effort to make the xTB Hamiltonian available in the DFTB+ program package.[1] DFTB+ supports a communication bridge to the tblite library when setting -DWITH_TBLITE=true at the CMake configuration step.

Note

Support in DFTB+ is available since version 21.2, released in fall 2021.

Installing DFTB+ and the tblite library#

A complete DFTB+ package is available via conda-forge. To install the conda package manager we recommend the miniforge installer. If the conda-forge channel is not yet enabled, add it to your channels with

conda config --add channels conda-forge

Once the conda-forge channel has been enabled, DFTB+ can be installed with:

conda install 'dftbplus=*=nompi_*'

Or to install the MPI enabled version, you can add mpich or openmpi as MPI provider or just let conda choose:

conda install 'dftbplus=*=mpi_*'

It is possible to list all of the versions available on your platform with:

conda search dftbplus --channel conda-forge

Now you are ready to use the dftb+ executable, find the tblite library is installed as well as part of the DFTB+ dependencies.

Input structure#

Input to DFTB+ is provided by creating a file named dftb_in.hsd in the custom human-friendly structured data (HSD) format, which is inspired by XML. The geometry input is provided in the Geometry group, either as xyzFormat for molecular geometries or as vaspFormat for periodic geometries. To enable the xTB methods the Hamiltonian group is set to xTB. In the xTB group the Method keyword is provided to select between GFN2-xTB, GFN1-xTB and IPEA1-xTB.

Molecular GFN2-xTB calculation#
Geometry = xyzFormat {
<<< "struc.xyz"
}

Hamiltonian = xTB {
  Method = "GFN2-xTB"
}

To perform periodic calculations with the xTB Hamiltonian only the k-point sampling has to be added to the xTB group with kPointsAndWeights. Using the SuperCellFolding provides Monkhorst–Pack k-point sampling.

Periodic GFN1-xTB calculation#
Geometry = vaspFormat {
<<< "POSCAR"
}

Hamiltonian = xTB {
  Method = "GFN1-xTB"
  kPointsAndWeights = SuperCellFolding {
    2   0   0
    0   2   0
    0   0   2
    0.5 0.5 0.5
  }
}

Instead of providing a Method the xTB method can be initialized from a parameter file by providing its path in ParameterFile.

# ...
Hamiltonian = xTB {
  ParameterFile = "gfn2-xtb.toml"
  # ...
}

Finally, to perform more than just single point calculations, the Driver group has to be provided. Best is to use the new GeometryOptimization driver, which defaults to a rational function minimizer as present in the xtb program package. For periodic structures the lattice optimization can be enabled by setting LatticeOpt to Yes.

Driver = GeometryOptimization {
  LatticeOpt = Yes
}

For the full capabilities for DFTB+ check the reference manual.

Literature#

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