LDA+U setup

To amend the description of electron correlations in local and semilocal XC functionals, up to 4 Hubbard U parameters can be defined for each species in the atom species section. For this optional ldaU XML elements have to be inserted into the respective section below the energyParameters, electronConfig, and nocoParams entries and above the lo entries. The following example demonstrates how an ldaU element looks like:

<ldaU l="2" U="8.0" J="0.9" l_amf="F"/>
Attribute Description
l The angular momentum quantum number of the orbital for which the U parameter is set.
U The U parameter in eV.
J The J parameter in eV.
l_amf This logical switch determines whether the "around mean field" limit (if true) or the atomic limit (if false) is used.

Mixing of the density matrix

Whenever a Hubbard U parameter is added to an atom not only the density has to be part of the mixing from iteration to iteration but the density matrix, too. For this additional parameters can be set in an optional ldaU XML element (different from the one above) in the calculationSetup section. Such an element looks like:

<ldaU l_linMix="F" mixParam="0.05" spinf="1.00"/>
Attribute Description
l_linMix This switch determines whether a straight mixing algorithm is applied to the density matrix (if true) or the mixing of the density matrix will be performed like the mixing of the density (if false). The switch is optional and set to false by default.
mixParam This is the optional mixing parameter that is used for the straight mixing of the density matrix. By default this parameter is 0.05.
spinf Optional, default ist 1.0.

If the ldaU element in the calculationSetup section is not present all parameters that can be set in it have their default values.

Further reading

  • The LDA+U method has been developed by Anisimov et al.
  • The implementation of LDA+U in Fleur is similar to the one proposed by Shick et al.
  • A comparison between the around mean field limit and the atomic limit is available in an article by Petukhov et al.