NOMEGA = integer (number of frequency points) NOMEGAR= integer (number of frequency points along real axis)default: NOMEGA 50, NOMEGAR = NOMEGA.
NOMEGA specifies the number of frequency grid points. Usually NOMEGAR (number of frequency points along real axis) equals NOMEGA. If NOMEGAR is smaller than NOMEGA (for instance 0), frequencies along the imaginary time axis are included (this feature is currently not fully supported).
Typically NOMEGA should be chosen around 50-100 (for the parallel version,
NOMEGA should be dividable by the number of compute nodes to obtain
maximum efficiency).
For quick and memory conserving calculations, it is sufficient to set
NOMEGA to values around NOMEGA= 20-30, but then you must expect errors
of the order of 20-50 meV for the gap, and 100-200 meV for
the bottom of the conduction band.
We furthermore recommend to increase NOMEGA not beyond 100
for a k-point sampling of
points/atom: the joint DOS and
the self-energy tend to posses spurious fine structure related
to the finite k-point grid. This fine structure is smoothed, when smaller
values for NOMEGA are used, or if more k-points are used.
For
k-points/atom NOMEGA can be usually increased
to 200-300 without noticing problems associated with this kind of noise.
Note that the spectral method ( LSPECTRAL, see Sec. 6.65.3) scales very favourable with respect to the number of frequency points, hence NOMEGA= 30 is usually only slightly faster than NOMEGA = 100.