Typical cases

We may distinguish the following typical cases for pw.x:

single-point (fixed-ion) SCF calculation.

Set calculation='scf'.

Namelists &IONS and &CELL need not to be present (this is the default). See Example 01.

band structure calculation.

First perform a SCF calculation as above; then do a non-SCF calculation specifying calculation='nscf', with the desired k-point grid and number nbnd of bands.

Specify nosym=.true. to avoid generation of additional k-points in low symmetry cases. Variables prefix and outdir, which determine the names of input or output files, should be the same in the two runs. See Example 01.

structural optimization.

Specify calculation='relax' and add namelist &IONS.

All options for a single SCF calculation apply, plus a few others. You may follow a structural optimization with a non-SCF band-structure calculation, but do not forget to update the input ionic coordinates. See Example 03.

molecular dynamics.

Specify calculation='md' and time step dt.

Use variable ion_dynamics in namelist &IONS for a fine-grained control of the kind of dynamics. Other options for setting the initial temperature and for thermalization using velocity rescaling are available. Remember: this is MD on the electronic ground state, not Car-Parrinello MD. See Example 04.

polarization via Berry Phase.

See Example 10, its README, and the documentation in the header of PW/bp_c_phase.f90.

Nudged Elastic Band calculation.

Specify calculation='neb' and add namelist &IONS.

All options for a single SCF calculation apply, plus a few others. In the namelist &IONS the number of images used to discretize the elastic band must be specified. All other variables have a default value. Coordinates of the initial and final image of the elastic band have to be specified in the ATOMIC_POSITIONS card. A detailed description of all input variables is contained in the file Doc/INPUT_PW. See also Example 17.

The output data files are written in the directory specified by variable outdir, with names specified by variable prefix (a string that is prepended to all file names, whose default value is: prefix='pwscf').

The execution stops if you create a file prefix.EXIT in the working directory. Note that just killing the process may leave the output files in an unusable state.