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, the nelectrons will be the sum of the arguments of NUP and NDOWN.
If the number of electrons is not specified in the parameter file, the default value will be chosen such that the system is charge neutral.