- the crystalline structure and symmetries.
- the set of k-points used.
- the exchange and correlation functional.
- convergency settings .
- possibly, PAW special settings.
- possibly, input variables for
spin-polarized systems and spin orbit coupling calculations.
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An example of a minimal input file to calculate the ground state of crystalline aluminium is given here:
# Crystalline aluminum. Calculation of the total energy # at fixed number of k points and broadening. #Definition of occupation numbers occopt 4 tsmear 0.05 #Definition of the unit cell acell 3*7.60 # This is equivalent to 7.60 7.60 7.60 rprim 0.0 0.5 0.5 # FCC primitive vectors (to be scaled by acell) 0.5 0.0 0.5 0.5 0.5 0.0 #Definition of the atom types ntypat 1 # There is only one type of atom znucl 13 # The keyword "znucl" refers to the atomic number of the # possible type(s) of atom. The pseudopotential(s) # mentioned in the "files" file must correspond # to the type(s) of atom. Here, the only type is Aluminum #Definition of the atoms natom 1 # There is only one atom per cell typat 1 # This atom is of type 1, that is, Aluminum xred 0.0 0.0 0.0 # This keyword indicate that the location of the atoms # will follow, one triplet of number for each atom # Triplet giving the REDUCED coordinate of atom 1. #Definition of the planewave basis set ecut 6.0 # Maximal kinetic energy cut-off, in Hartree pawecutdg 10.0 #Maximal kinetic energy cut-off, in Hartree for the fine grid in case of PAW calculation #Definition of the k-point grid ngkpt 2 2 2 # This is a 2x2x2 FCC grid, based on the primitive vectors chksymbreak 0 #Definition of the SCF procedure nstep 10 # Maximal number of SCF cycles toldfe 1.0d-6 # Will stop when, twice in a row, the difference # between two consecutive evaluations of total energy # differ by less than toldfe (in Hartree) # This value is way too large for most realistic studies of materials