This keyword determines the maximum size of the g-vectors included in the fine grid.
The fine grid is set up such that all g-vectors with |g| less than or equal to FINE_GMAX are included.
-1 a0-1 - this results in the fine and standard grids being identical
FINE_GMAX : 20 1/ang
There is a more convenient way of dealing with fine grid using dimensionless parameter
FINE_GRID_SCALE which defines
FINE_GMAX in terms of standard grid
CASTEP keyword glossary
CASTEP parameters keywords