NBANDSO: Difference between revisions
(Created page with "{{TAGDEF|NBANDSO|[integer]}} Description: {{TAG|NBANDSO}} determines how many occupied orbitals are included in the BSE calculations. ---- The compute time for BSE and Cass...") |
No edit summary |
||
| Line 17: | Line 17: | ||
VASP always uses the orbitals closest to the Fermi-level, and {{TAG|NBANDSO}} (<math>N_{\mathrm{occ}}</math>) and {{TAG|NBANDSV}} (<math>N_{\mathrm{virtual}}</math>) determines how many occupied and unoccupied orbitals are included. The defaults are fairly "conservative" and equal the total number of electrons/2 (this usually implies that all occupied state are included). For highly accurate results, {{TAG|NBANDSV}} often needs to be increased, whereas for large systems one is often forced to reduce both values to much smaller numbers. Sometimes qualitative results for band like Wannier-Mott excitons can be obtained even with a single conduction and valence band. | VASP always uses the orbitals closest to the Fermi-level, and {{TAG|NBANDSO}} (<math>N_{\mathrm{occ}}</math>) and {{TAG|NBANDSV}} (<math>N_{\mathrm{virtual}}</math>) determines how many occupied and unoccupied orbitals are included. The defaults are fairly "conservative" and equal the total number of electrons/2 (this usually implies that all occupied state are included). For highly accurate results, {{TAG|NBANDSV}} often needs to be increased, whereas for large systems one is often forced to reduce both values to much smaller numbers. Sometimes qualitative results for band like Wannier-Mott excitons can be obtained even with a single conduction and valence band. | ||
== Related Tags and Sections == | |||
{{TAG|NBANDSV}} | |||
---- | ---- | ||
[[The_VASP_Manual|Contents]] | [[The_VASP_Manual|Contents]] | ||
[[Category:INCAR]] [[Category:BSE]] | [[Category:INCAR]] [[Category:BSE]] | ||
Revision as of 15:45, 16 January 2017
NBANDSO = [integer]
Description: NBANDSO determines how many occupied orbitals are included in the BSE calculations.
The compute time for BSE and Cassida type calculations growswith the third power of the number of included occupied and unoccupied bands
and the memory requirements increase quadratically
Please be aware that symmetry is not exploited in the BSE code, hence memory requirements can be excessive. To allow for calculations on large systems, the BSE code distributes the BSE matrix among all available cores, and uses scaLAPACK for the diagonalization.
VASP always uses the orbitals closest to the Fermi-level, and NBANDSO () and NBANDSV () determines how many occupied and unoccupied orbitals are included. The defaults are fairly "conservative" and equal the total number of electrons/2 (this usually implies that all occupied state are included). For highly accurate results, NBANDSV often needs to be increased, whereas for large systems one is often forced to reduce both values to much smaller numbers. Sometimes qualitative results for band like Wannier-Mott excitons can be obtained even with a single conduction and valence band.