4.5 what='scf_nk'

With this option the code makes several self-consistent calculations, in parallel on several images, varying the size of the k-point grid, and optionally for metals the smearing parameter degauss. In the input of pw.x the minimum value of these parameters is given and these values are increased in fixed intervals controlled by the following variables. On output the energy is plotted as a function of the mesh size, one curve for each smearing parameter.
The variables that control this option are:

nnk        : the number of different values of nk to test
             Default: integer 5
deltank(3) : the interval between nk values. All three values of nk1, nk2, and
             nk3 are updated simultaneously.
             Default: integer 2  2  2
nsigma     : the number of smearing intervals.
             Default: integer 1 
deltasigma : the distance between different smearing values.
             (can be either positive or negative)
             Default: 0.005 Ry
flnkconv   : file where the data with the k point convergence is written
             Default: character(len=*) 'output_nkconv.dat'
flpsnkconv : name of the postscript file with the k points convergence plot.
             Default: character(len=*) 'output_nkconv'

An example for this option can be found in example11.
Number of tasks for this option: nnk * nsigma.