## zigzag

### Syntax

zigzag boolean_x boolean_y boolean_z

• boolean_x, boolean_y, boolean_z = t or f

  t is true
f is false


### Examples

zigzag t f f
zigzag t t t


### Description

This command decides whether the simulation cell boundaries are left zigzagged along the x, y, and z directions, respectively.

Due to the rhombohedral shape of the finite elements in the coarse-grained domain, the simulation cell mostly likely has zigzagged boundaries, as shown in Fig. C27(a) of Xu et al., 2015. On the other hand, flat boundaries are sometimes desirable to enforce the periodic boundary conditions or to lower the aphysical stress concentrations at the boundaries.

If one of the three booleans in this command is f, atoms will be filled in the corresponding jagged interstices, resulting in flat boundaries normal to the corresponding direction, unless the boundaries were already flat with rhomboheral elements, e.g., parallel to a {111} plane in an FCC lattice or to a {110} plane in a BCC lattice. Examples of the filled atoms include Fig. C27(b) of Xu et al., 2015 and the figure for the subdomain command in which the atoms are filled in at the leftmost and rightmost simulation cell boundaries. If a certain boolean is t, no atoms will be filled in at the boundaries.

When a boundary is periodic, the corresponding zigzag boolean becomes f, regardless of what is set in this command, because the periodic boundaries must be flat in CAC simulations.

This command becomes irrelevant when boolean_restart = t, in which case there is no need for the boundary shape information.

model_init.f90

### Default

zigzag t t t