CSHIFT: Difference between revisions
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{{TAGDEF|CSHIFT|[real]}} | {{TAGDEF|CSHIFT|[real]}} | ||
{{DEF|CSHIFT|{{TAG|OMEGAMAX}}*1.3 / max({{TAG|NOMEGA}},40)| for [[GW calculations]] |0.1| for | {{DEF|CSHIFT|0.1| for {{TAG|LOPTICS}} |{{TAG|OMEGAMAX}}*1.3 / max({{TAG|NOMEGA}},40)| for [[GW calculations]]|0.1| for [[BSE calculations]]/[[Time-dependent_density-functional_theory_calculations|Casida TDDFT calculations]]|0.1| for [[Time Evolution|Time Evolution TDDFT calculations]]}} | ||
Description: {{TAG|CSHIFT}} sets the | Description: {{TAG|CSHIFT}} sets a Lorentzian broadening in eV of the dielectric tensor via the complex shift η in the [[LOPTICS#kramerskronig|Kramers-Kronig transformation]] of the response function. | ||
---- | ---- | ||
The default {{TAG|CSHIFT}}=0.1 is perfectly acceptable for most calculations and causes a slight smoothing of the real part of the dielectric function. If the gap is very small (i.e. approaching two times {{TAG|CSHIFT}}), slight inaccuracies in the static dielectric constant are possible, which can be remedied by decreasing {{TAG|CSHIFT}}. If {{TAG|CSHIFT}} is further decreased, it is strongly recommended to increase the | The default {{TAG|CSHIFT}}=0.1 is perfectly acceptable for most calculations and causes a slight smoothing of the real part of the dielectric function. If the gap is very small (i.e. approaching two times {{TAG|CSHIFT}}), slight inaccuracies in the static dielectric constant are possible, which can be remedied by decreasing {{TAG|CSHIFT}}. If {{TAG|CSHIFT}} is further decreased, it is strongly recommended to increase the frequency grid by setting {{TAG|NEDOS}} to values around 2000. | ||
{{NB|mind|For the quartic-scaling GW algorithm, one should manually check that {{TAG|CSHIFT}} is at least as large as the grid spacing at low frequencies. If {{TAG|CSHIFT}} is smaller than the grid spacing, the QP energies might show erratic behavior (for instance large re-normalization factors Z).}} | |||
For GW | |||
as the grid spacing at low frequencies. If {{TAG|CSHIFT}} is smaller than the grid spacing, | |||
the QP energies might show erratic behavior (for instance large re-normalization factors Z). | |||
== Related tags and articles == | == Related tags and articles == | ||
{{TAG|OMEGAMIN}}, | {{TAG|OMEGAMIN}}, | ||
{{TAG|OMEGAMAX}}, | {{TAG|OMEGAMAX}}, | ||
{{TAG|LOPTICS}}, | {{TAG|LOPTICS}}, | ||
{{sc|CSHIFT|Examples|Examples that use this tag}} | {{sc|CSHIFT|Examples|Examples that use this tag}} | ||
Revision as of 09:59, 17 October 2024
CSHIFT = [real]
| Default: CSHIFT | = 0.1 | for LOPTICS |
| = OMEGAMAX*1.3 / max(NOMEGA,40) | for GW calculations | |
| = 0.1 | for BSE calculations/Casida TDDFT calculations | |
| = 0.1 | for Time Evolution TDDFT calculations |
Description: CSHIFT sets a Lorentzian broadening in eV of the dielectric tensor via the complex shift η in the Kramers-Kronig transformation of the response function.
The default CSHIFT=0.1 is perfectly acceptable for most calculations and causes a slight smoothing of the real part of the dielectric function. If the gap is very small (i.e. approaching two times CSHIFT), slight inaccuracies in the static dielectric constant are possible, which can be remedied by decreasing CSHIFT. If CSHIFT is further decreased, it is strongly recommended to increase the frequency grid by setting NEDOS to values around 2000.
| Mind: For the quartic-scaling GW algorithm, one should manually check that CSHIFT is at least as large as the grid spacing at low frequencies. If CSHIFT is smaller than the grid spacing, the QP energies might show erratic behavior (for instance large re-normalization factors Z). |