Exchange-Correlation functionals

	Core NanoLanguage elements
electronDensityParameters	executeSelfConsistentCalculation

Name

Exchange-correlation functionals — Determines which approximation to use for the exchange-correlation functional.

Synopsis

Namespace: ATK.KohnSham or ATK.TwoProbe

Description

The main approximation in ATK is related to the exchange-correlation functional. ATK supports three different functionals, as listed below. In general, structural properties do not depend much on the exchange-correlation functional, while energy changes are more sensitive. The GGA functionals will usually perform better than the LDA functional, with GGA.revPBE being the preferred choice.

The three types of exchange-correlation functionals available in ATK are:

LDA.PZ: The local density approximation (LDA) with the Perdew-Zunger parametrization [9] of the correlation energy of a homogeneous electron gas calculated by Ceperley-Alder [5].
GGA.PBE: Perdew-Burke-Ernzerhof parametrization of the generalized gradient approximation (GGA) [8].
GGA.revPBE: Revised Perdew-Burke-Ernzerhof parametrization of the GGA [16]

These are available in both spin-unpolarized and spin-polarized forms.

Usage examples

Create a KohnShamMethod object method using the LDA Perdew-Zunger parametrization in unpolarized form:

method = KohnShamMethod(exchange_correlation_type = LDA.PZ)

Create a KohnShamMethod object using the Perdew-Burke-Ernzerhof parametrization of GGA in spin-polarized form:

initial_density = electronDensityParameters(
    initial_spin = 1.0*hbar
    ) 
method = KohnShamMethod(
    exchange_correlation_type = GGA.PBE,
    electron_density_parameters = initial_density
    )

Notes

See electronDensityParameters() for more information regarding spin-polarization. The default functional in ATK is LDA.PZ, which offers slightly better performance (at the cost of accuracy).

Each exchange-correlation functional employs its own set of pseudo-potentials for all periodic elements. It is possible to specify a custom pseudo-potential for each element using the pseudoPotentialParameters().

Further examples


electronDensityParameters		executeSelfConsistentCalculation