NBANDS (.param)

Keyword type

Integer

This keyword determines the maximum number of bands at any k-point and spin.

There are three ways in which you can specify the maximum number of bands at any k-point and spin:

Directly, using NBANDS.
Indirectly, by specifying the number of extra bands in addition to the number of occupied bands using 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 PERC_EXTRA_BANDS.

It is not possible to have both the NBANDS keyword and either the NEXTRA_BANDS or PERC_EXTRA_BANDS keywords present in the same input file.

If NEXTRA_BANDS is specified and SPIN_POLARIZED : FALSE:

	NBANDS : (NELECTRONS/2) + NEXTRA_BANDS

Or, if SPIN_POLARIZED : TRUE:

	NBANDS : max(NUP, NDOWN) + NEXTRA_BANDS.

	NBANDS : (NELECTRONS/2) × [ 1 + (PERC_EXTRA_BANDS/100)]

Or, if SPIN_POLARIZED : TRUE:

	NBANDS : max(NUP, NDOWN) × [ 1 + (PERC_EXTRA_BANDS/100)]

If NBANDS, NEXTRA_BANDS and PERC_EXTRA_BANDS are not specified and FIX_OCCUPANCY : TRUE, then, if SPIN_POLARIZED : FALSE:

	NBANDS : NELECTRONS/2.

Or, if SPIN_POLARIZED : TRUE:

	NBANDS : max(NUP, NDOWN)

If FIX_OCCUPANCY : FALSE, these default values of NBANDS will be multiplied by 1.2.

NBANDS : 64