Use the Boundary Pair node to set the periodicity conditions over the boundaries of the Cell Periodicity domain. This node is only available when the Boundary condition type in the Cell Periodicity parent feature is set to Periodic temperature. In 2D, at least two such pairs are needed, and in 3D at least three pairs. The number of pairs depends on the shape of the unit cell.

Select all corresponding boundaries belonging to both sides of the pair. The source and destination sides of the pairs can be manually specified by adding a Manual Destination Selection subnode.

To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.

The Constraint settings can be set to Pointwise constraints (default), Weak constraints or Nitsche constraints.

Physics tab with Cell Periodicity node selected in the model tree: