# PP Card

This card defines the phase shift of the excitation between one unit cell and the next for periodic boundary conditions. The unit cell for a PBC calculation is specified with the PE card.

On the Home tab, in the Planes / arrays group, click the Periodic boundary icon. From the drop-down list, click the Periodic phase (PP) icon.

## Parameters:

- Manually specify phase shift
- The phase shift is manually specified.
- Determine phase shift from plane-wave excitation
- When a plane wave is used as excitation the phase difference between the cells cannot be specified, but is determined by the excitation.
- Determine phase shift from beam pointing (
squint

) angle: - The phase shift is determined by specifying the theta and phi angle of the
squint

angle. - Phase shift in ${\widehat{u}}_{1}$ direction (degrees)
- Phase shift in the first direction, ${\widehat{u}}_{1}$ .
- Phase shift in ${\widehat{u}}_{2}$ direction (degrees)
- Phase shift in the second direction, ${\widehat{u}}_{2}$ .

## One dimension:

- Theta angle (degrees)
- Orientation of the squint angle. The angle, theta, in degrees is the angle between the squint angle and the plane defined by the ${\widehat{u}}_{1}$ vector.

## Two dimensions:

- Theta angle (degrees)
- Orientation of the squint angle. The angle, theta, in degrees is the angle between the squint angle and the ${u}_{1}=0$ plane.
- Phi angle (degrees)
- Orientation of the squint angle. The angle, phi, in degrees is the angle between the squint angle and the plane defined by the ${\widehat{u}}_{1}$ vector.