Recommended minimum setup

Although the previous calculations can be performed using an empty INCAR file it is recommended to specify a few parameter always manually

PREC = Normal              #  precision normal
ENCUT = 300                #  cutoff used throughout all calculations
LREAL = .FALSE.  or Auto   #  real space projection yes / no
ISMEAR = 0 or 1 or -5      #  method to determine partial occupancies

These four parameters should be present in all calculations. They completely control the technical accuracy of the calculations in particular the basis sets ( ENCUT), and wether the real space projection scheme is used or not. Total energies of two calculations should be only compared and subtracted, if the first three parameters are set identically in both calculations. Ideally the parameter ISMEAR should be also identical throughout all calculations (but this might be difficult in some cases).