3 Input data

Input data for cp.x is organized into several namelists, followed by other fields (``cards'') introduced by keywords. The namelists are

&CONTROL:	general variables controlling the run
&SYSTEM:	structural information on the system under investigation
&ELECTRONS:	electronic variables, electron dynamics
&IONS :	ionic variables, ionic dynamics
&CELL (optional):	variable-cell dynamics

The &CELL namelist may be omitted for fixed-cell calculations. This depends on the value of variable calculation in namelist &CONTROL. Most variables in namelists have default values. Only the following variables in &SYSTEM must always be specified:

ibrav	(integer)	Bravais-lattice index
celldm	(real, dimension 6)	crystallographic constants
nat	(integer)	number of atoms in the unit cell
ntyp	(integer)	number of types of atoms in the unit cell
ecutwfc	(real)	kinetic energy cutoff (Ry) for wavefunctions.

).

Explanations for the meaning of variables ibrav and celldm, as well as on alternative ways to input structural data, are contained in files Doc/INPUT_CP.*. These files are the reference for input data and describe a large number of other variables as well. Almost all variables have default values, which may or may not fit your needs.

Comment lines in namelists can be introduced by a "!", exactly as in fortran code.

After the namelists, you have several fields (``cards'') introduced by keywords with self-explanatory names:

ATOMIC_SPECIES
ATOMIC_POSITIONS
CELL_PARAMETERS (optional)
OCCUPATIONS (optional)

The keywords may be followed on the same line by an option. Unknown fields are ignored. See the files mentioned above for details on the available ``cards''.

Comments lines in ``cards'' can be introduced by either a ``!'' or a ``#'' character in the first position of a line.