### Specifying an electron configuration

Within each species in the atomSpecies section an electronConfig element can be defined. This is used to declare which electron states are to be treated within the core electron framework and which have to be considered in the valence electron framework. Occupations for the different electron states are also set here. The electronConfig element is optional and only required if a setup differing from the default for the respective atom shall be considered. The following example demonstrates how an electron configuration is set:

<electronConfig>
<coreConfig>[Xe] (4f5/2) (4f7/2)</coreConfig>
<valenceConfig>(6s1/2) (5d3/2) (5d5/2) (6p1/2) (6p3/2)</valenceConfig>
<stateOccupation state="(6p3/2)" spinUp="1.00" spinDown="1.00"/>
</electronConfig>

The electronConfig encloses the XML elements coreConfig, valenceConfig and possibly multiple stateOccupation elements.

The coreConfig element is used to provide a space separated list of electron states to be treated by the core framework. Certain subsets can be set in terms of noble gas configurations. The electron states together with the noble gas configurations are

noble gas configuration electron states
[He] (1s1/2)
[Ne] (2s1/2) (2p1/2) (2p3/2)
[Ar] (3s1/2) (3p1/2) (3p3/2)
[Kr] (4s1/2) (3d3/2) (3d5/2) (4p1/2) (4p3/2)
[Xe] (5s1/2) (4d3/2) (4d5/2) (5p1/2) (5p3/2)
[Rn] (6s1/2) (4f5/2) (4f7/2) (5d3/2) (5d5/2) (6p1/2) (6p3/2)
(7s1/2) (5f5/2) (5f7/2) (6d3/2) (6d5/2)

In the table each noble gas configuration incorporates the electron states that are stated in the same line and the lines above.

In the valenceConfig element a similar list of electron states has to be provided to declare the occupied valence states. Here noble gas configurations are not allowed.

For each of the listed states that is not fully occupied a stateOccupation element has to be set. In it the state attribute selects the respective states. The spinUp and spinDown attributes are used to define the number of electrons in the two spin channels.