Editing Boundary conditions (section)

== Infinite 2D geometries ==

In infinite 2D lattice geometries the outside part of the geometry is composed of a single cell filling the space outside the surface at which the boundary conditions are applied. For example:

 <nowiki>
cell 999 0 outside  b1</nowiki>

where surface b1 is an infinite square prism. 

Two types of infinite square lattices created using reflective and periodic boundary conditions are illustrated below, together with a non-repetitive black boundary. The geometry plot is extended beyond the outermost surface, in which case the plot shows the vacuum region as black and applies reflections and translations accordingly. The image captions provide links to particle track animations, which illustrate the behaviour when the boundary is hit. It should be noted that the boundary surface itself is not plotted, since the material is the same on both sides.

<gallery mode="nolines" widths=320px heights=320px>
Image:vacu2D.png|'''Vacuum boundary conditions''' ("set&nbsp;bc&nbsp;1", xy-plot). See [[media:vacu2D.gif|animated particle tracks]].
Image:refl2D.png|'''Reflective boundary conditions''' ("set&nbsp;bc&nbsp;2", xy-plot). See [[media:refl2D.gif|animated particle tracks]].
Image:peri2D.png|'''Periodic boundary conditions''' ("set&nbsp;bc&nbsp;3", xy-plot). See [[media:peri2D.gif|animated particle tracks]].
</gallery>

Serpent allows using reflective and periodic boundary conditions for both square and hexagonal prisms, although it should be noted that a reflective boundary with a non-symmetrical hexagonal cell makes physically no sense.