# PERIODIC

References: Guidon2008, Guidon2009

Sets up periodic boundary condition parameters if requested [Edit on GitHub]

## Keywords

- NUMBER_OF_SHELLS

## Keyword descriptions

NUMBER_OF_SHELLS: integer = -1

  Usage: NUMBER_OF_SHELLS 2

  Number of shells taken into account for periodicity. By default, cp2k tries to automatically evaluate this number. This algorithm might be to conservative, resulting in some overhead. You can try to adjust this number in order to make a calculation cheaper. [Edit on GitHub]