This holds the cut off energy for the plane wave basis set being used in the current calculation.
If the BASIS_PRECISION keyword is defined in the parameter file, the
cut off energy will be equal to the highest of the cut off energies
associated with the chosen level of accuracy for the pseudopotentials
used in the calculation. This will be set by the ion_initialise
subroutine.
If neither BASIS_PRECISION nor CUT_OFF_ENERGY are defined in the parameter file, the default cut off energy is that associated with the FINE level of accuracy for the pseudopotentials in the calculation.
If the CUT/SMALL>_OFF/SMALL>_ENERGY keyword is not present in the input file, this
parameter will be set to -1 Ha until the correct value is assigned by the
ion_initialise subroutine.