NOMEGA= [integer] (number of frequency points)
NOMEGAR= [integer] (number of frequency points along real axis)
Default: | ||
NOMEGA | =50 | for calculations |
NOMEGAR | =NOMEGA | |
NOMEGA | =12 | for ACFDT calculations |
NOMEGAR | =0 |
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 one 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 related to the spurious noise.
Note that the spectral method (LSPECTRAL, see Sec. 6.73.4) scales very favourable with respect to the number of frequency points, hence NOMEGA=30 is usually only slightly faster than NOMEGA=100-200.