OPTICS_NBANDS (.param)

Keyword type

Integer

This keyword determines the number of bands at each k-point when performing an optical spectrum calculation.

There are three ways in which you can specify the number of bands at each k-point:

Directly, using OPTICS_NBANDS.
Indirectly, by specifying the number of extra bands in addition to the number of occupied bands using OPTICS_NEXTRA_BANDS.
This is the method used in the CASTEP interface.
Indirectly, by specifying the number of extra bands in addition to the number of occupied bands as a percentage of the latter value using OPTICS_PERC_EXTRA_BANDS.

It is not possible to have both the OPTICS_NBANDS keyword and either the OPTICS_NEXTRA_BANDS or OPTICS_PERC_EXTRA_BANDS keywords present in the same input file.

If OPTICS_NBANDS is present in the parameter file, the value of BS_NBANDS is determined by this keyword.

If OPTICS_NEXTRA_BANDS is present in the parameter file:

	BS_NBANDS : max(NUP, NDOWN) + OPTICS_NEXTRA_BANDS.

If OPTICS_PERC_EXTRA_BANDS is present in the parameter file:

	BS_NBANDS : max(NUP, NDOWN) x [1 + OPTICS_PERC_EXTRA_BANDS/100)].

The default value of this parameter is 3 × NBANDS.

OPTICS_NBANDS : 192