This keyword specifies the total number of electrons in the system.
If the CHARGE keyword is specified, NELECTRONS will be chosen such that the total system charge is equal to the argument of CHARGE.
Alternatively, if NUP and NDOWN are specified, NELECTRONS will be the sum of the arguments of NUP and NDOWN.
If the number of electrons is not specified, a default value will be chosen such that the system is charge neutral.
NELECTRONS : 3
CASTEP keyword glossary
CASTEP parameters keywords