calculateFermiEnergy

	Core NanoLanguage elements
calculateEnergyBands	calculateMolecularEnergySpectrum

Name

calculateFermiEnergy — Calculates the Fermi energy for a molecular or bulk system.

Synopsis

Namespace: ATK.KohnSham

PhysicalQuantity calculateFermiEnergy(self_consistent_calculation)

Description

Returns the self-consistent Fermi energy of a molecular or bulk calculation as a PhysicalQuantity.

In ATK, the Fermi energy is calculated by requiring the system to be charge neutral. More precisely, the Fermi level is the energy which makes the Fermi occupation of the orbitals equal to the number of electrons in the system.

List of arguments

self_consistent_calculation

An object returned from a previously performed self-consistent calculation for a MoleculeConfiguration or a BulkConfiguration.

Default: None

Usage examples

from ATK.KohnSham import *
...
dft_calculation = dft_method.apply(water_molecule)
energy = calculateFermiEnergy( dft_calculation )
print "Fermi energy = %g eV" % ( energy.inUnitsOf(eV) )

Notes

There is a common Fermi level for spin-up and spin-down electrons in spin-dependent calculations.

The Fermi level is the energy zero-level for eigenenergies returned when calculating band structures.

For molecules, the Fermi level can vary dramatically as a function of the temperature and other parameters, and is thus not really well-defined. It is then physically more interesting to look at the HOMO level.

For molecular systems, the Fermi level is reported relative to the vacuum level, and is used to determine the eigenstate occupations of the molecular energy levels.

For bulk systems, the vacuum level is not well defined, and so in this case the energy zero is arbitrary. The absolute value of the Fermi energy can however be used to evaluate the work function, since the same (arbitrary) zero-level is used to define the effective potential.


calculateEnergyBands		calculateMolecularEnergySpectrum