# SplitInterstitial¶

class SplitInterstitial(interstitial_element, site_element, site_index, unit_cell_index=None, cartesian_coordinates=None, fractional_coordinates=None)

Data structure for a split interstitial (dumbbell) defect. This class only holds information and does not check for physical validity, which is imposed by SplitInterstitialList during dumbbell generation. The two sets of cartesian_coordinates (or fractional_coordinates) are symmetric with respect to site_index.

Parameters: interstitial_element (PeriodicTableElement) – The element to add at the given positions. site_element (PeriodicTableElement) – The lattice site displaced by the an interstitial element. site_index (int) – The index of the atom in the bulk unit cell configuration to be substituted with a split interstitial defect. Default: 0 unit_cell_index (sequence on int (size 3)) – The index of the unit cell in the infinite crystal which the reference site belogs to. substituted with a split interstitial defect. Default: (0, 0, 0) cartesian_coordinates (PhysicalQuantity of type length (size 2x3) | None) – Positions at which to insert two atoms of the split interstitial defect, given in absolute coordinates. This option is mutually exclusive to fractional_coordinates. Default: None fractional_coordinates (numpy.array (size 2x3) | None) – Positions at which to insert two atoms of the split interstitial defect, given in fractional coordinates of the bulk unit cell. This option is mutually exclusive to cartesian_coordinates. Default: None
cartesianCoordinates()
Returns: The coordinates of the split interstitial defect as Cartesian coordinates if they have been specified, otherwise returns None. PhysicalQuantity of type length (size 2x3) | None
defectList()
Returns: The list of constituent defects. list of [Vacancy | Substitutional | Interstitial]
element()
Returns: The interstitial element used in the split-interstitial defect. int
fractionalCoordinates()
Returns: The coordinates of the split interstitial defect as fractional coordinates if they have been specified, otherwise returns None. numpy.array (size 2x3) | None
siteIndex()
Returns: Index of the site being replaced by a split interstitial defect int

## Notes¶

A split interstitial is a type of defect occurring in solids. It is created by introducing an impurity interstitial_element that displaces an atom of the lattice. The pair of impurity and displaced atom is commonly referred to as a dumbbell for its resemblance to the weight-lifting device, as seen in Fig. 154.

Fig. 154 Split-interstitial on GaAs. One As atom of the crystal is replaced with two atoms of the same species. This dumbbell defect is centered at the site of the original atom.