|NELECT||=||- (number of valence electrons)|
NELECT = number of electrons
Usually you should not set this line -- the number of electrons is determined automatically from POTCAR (ZVAL of the element) and POSCAR (number of the atoms of the respective atom type).
If the number of electrons is not compatible with the number derived from the valence and the number of atoms a homogeneous background-charge is assumed.
If the number of ions specified in the POSCAR file is 0 and NELECT=n, then the energy of a homogeneous LDA-electron gas is calculated.