This keyword specifies the cutoff energy for the plane wave basis sets that will be used in the calculation.
If the BASIS_PRECISION is defined, the cutoff energy will be equal to the highest of the cutoff energies associated with the chosen level of accuracy, for the pseudopotentials used in the calculation.
If neither the BASIS_PRECISION nor the CUT_OFF_ENERGY are defined, the default cutoff energy is that associated with the FINE level of accuracy, for the pseudopotentials in the calculation.
It is not possible to specify both the BASIS_PRECISION and the CUT_OFF_ENERGY in a single file.
CUT_OFF_ENERGY = 125 eV
CASTEP keyword glossary
CASTEP parameters keywords