DFTBDirectory¶

class DFTBDirectory(path)¶

Class for representing a DFTB parameter file directory.

Parameters:: path (str) – The path of the directory to read files from.

fillingMethod(element)¶

Parameters:: element (PeriodicTableElement) – The element for which to query the filling method.
Returns:: The method used for setting up the initial occupation for the given element.
Return type:: SphericalSymmetric | Anisotropic

onsiteSpinOrbitSplit(element)¶

Query the onsite spin-orbit split energies for a given element.

Parameters:: element (PeriodicTableElement) – The element for which to query the spin-orbit split energies.
Returns:: The onsite spin-orbit split for this element.
Return type:: PhysicalQuantity of type energy

onsiteSpinSplit(element)¶

Query the onsite spin-split energies for a given element.

Parameters:: element (PeriodicTableElement) – The element for which to query the spin splits.
Returns:: The onsite spin-split energies for this element as a square matrix of size n where n is the number of subshells of the given element.
Return type:: PhysicalQuantity of type energy

pairPotentials(configuration)¶

Query function for getting the pair potentials.

Parameters:: configuration (MoleculeConfiguration | BulkConfiguration | DeviceConfiguration | SurfaceConfiguration) – The configuration defining which elements to load.
Returns:: The pair-potentials.
Return type:: list of PairPotential

setFillingMethod(element, filling_method)¶

Set the method used for setting up the initial occupation for the given element.

Parameters:

element (PeriodicTableElement) – The element for which to set the filling method.
filling_method (SphericalSymmetric | Anisotropic) – The method used for setting up the initial occupation.

setOnsiteSpinOrbitSplit(element, split)¶

Set the onsite spin-orbit split energies for a given element in the configuration.

Parameters:

element (PeriodicTableElement) – The element for which to set the spin-orbit splits.
split (PhysicalQuantity of type energy) – The onsite spin-split energies for this element as a square matrix of size n where n is the number of subshells of the given element.

setOnsiteSpinSplit(element, split)¶

Set the onsite spin split energies for a given element in the configuration.

Parameters:

element (PeriodicTableElement) – The element for which to set the spin splits.
split (PhysicalQuantity of type energy) – The on-site spin-split energies for each subshell pair of the element.

setVacuumLevel(element, vacuum_level)¶

Set the energy shift of the vacuum level for a given element.

Parameters:

element (PeriodicTableElement) – The element for which to set the energy shift of the vacuum level.
vacuum_level (PhysicalQuantity of type energy) – The energy shift of the vacuum level.

table(configuration)¶

Query function for getting the SlaterKosterTable representation of the parameter files in the directory.

Parameters:: configuration (MoleculeConfiguration | BulkConfiguration | DeviceConfiguration | SurfaceConfiguration) – The configuration defining which elements to load.
Returns:: A SlaterKosterTable instance representing the parameter files in the directory.
Return type:: SlaterKosterTable

vacuumLevel(element)¶

Parameters:: element (PeriodicTableElement) – The element for which to query the energy shift of the vacuum level.
Returns:: The energy shift of the vacuum level for the given element.
Return type:: PhysicalQuantity of type energy

Usage Examples¶

Set up a self-consistent tight-binding calculation using parameters in the format developed by the DFTB consortium.

# Set up a graphene crystal
bulk_configuration = BulkConfiguration(
    bravais_lattice=Hexagonal(2.4612*Angstrom, 6.709*Angstrom),
    elements=[Carbon, Carbon],
    cartesian_coordinates=[[ 0.        ,  0.        ,  0.        ],
                         [ 1.2306    ,  0.71050145,  0.        ]]*Angstrom
    )

# setup slater-koster calculator with dftb parameters

basis_set = DFTBDirectory("dftb")

pair_potentials = DFTBDirectory("/dftb")

numerical_accuracy_parameters = NumericalAccuracyParameters(
    k_point_sampling=(4, 4, 1) )

calculator = SlaterKosterCalculator(
    basis_set=basis_set,
    pair_potentials=pair_potentials,
    numerical_accuracy_parameters=numerical_accuracy_parameters,
    )
bulk_configuration.setCalculator(calculator)

initial_velocity = MaxwellBoltzmannDistribution(
        temperature=1000.0*Kelvin
    )

method = NVEVelocityVerlet(
        time_step=1.0*femtoSecond,
        initial_velocity=initial_velocity
    )

molecular_dynamics = MolecularDynamics(
        bulk_configuration,
        constraints=[],
        trajectory_filename='trajectory.nc',
        steps=50,
        log_interval=1,
        method=method
    )

Notes¶

QuantumATK can auto detect parameters stored in the directory share/tightbinding/dftb in the QuantumATK installation directory.
Only some parameter sets include a spin-polarization splitting \(W\). If this information is missing you can use the built-in database (see Spin polarization).
The highest angular momentum per each element is officially not part of the DFTB Slater-Koster file format. However, some codes use the convention to parse this information from the third integer (s=1, p=2, d=3) in the first row of the onsite file. We follow the same convention. When the value is not present in the file, as a fall back we determine it by inspecting non-zero interactions.