LSPECTRALGW: Difference between revisions

Latest revision as of 10:12, 19 July 2022

LSPECTRALGW = .FALSE. | .TRUE.
Default: LSPECTRALGW = .FALSE.

Description: LSPECTRALGW specifies to use the spectral method for calculating the self-energy.

If LSPECTRALGW = .TRUE. is set, the imaginary part of the self-energy $\Sigma(\omega)= G W$ is calculated from the imaginary part of screened potential $W(\omega)$ by shifting the poles of $W$ by $\pm \epsilon$ , where $\epsilon$ are the poles of the Green's function $G$ . Generally, LSPECTRALGW affects the compute time very little. QP energies also hardly change when LSPECTRALGW is modified. However, LSPECTRALGW = .TRUE. is usually slightly more robust, and should be selected for molecules and other systems with flat dispersion-less bands. One the other hand, LSPECTRALGW = .TRUE. seems to converge slightly slower, as the complex shift CSHIFT is decreased. Set this flag, if the QP energies show erratic behavior, for instance, if QP energies or Z-factors are not in the expected range of values (0.5<Z<0.9).

@@ Line 1: / Line 1: @@
-{{TAGDEF|LSPECTRALGW|.FALSE. {{!}} .TRUE.}}
+{{TAGDEF|LSPECTRALGW|.FALSE. {{!}} .TRUE.|.FALSE.}}
-{{DEF|LSPECTRALGW|.TRUE.|if {{TAG|NOMEGA}}>2}}
-Description: {{TAG|LSPECTRALGW}} specifies to use the spectral method.
+Description: {{TAG|LSPECTRALGW}} specifies to use the spectral method for calculating the self-energy.
 ----
-If {{TAG|LSPECTRALGW}} = .TRUE. is set, the imaginary part of the independent particle polarizability <math>\chi_{\mathbf{q}}^0 (\mathbf{G}, \mathbf{G}', \omega)</math> is calculated first, and afterwards the full independent particle polarizability is determined using a Kramers-Kronig (or Hilbert) transform. This reduces the computational work load by almost a factor {{TAG|NOMEGA}}/2. The downside of the coin is that the response function must be kept in memory for all considered frequencies, which can cause excessive memory requirements. VASP therefore distributes the dielectric functions among the available compute nodes.
+If {{TAG|LSPECTRALGW}} = .TRUE. is set, the imaginary part of the self-energy <math>\Sigma(\omega)= G W</math> is calculated from the imaginary part of screened potential <math>W(\omega)</math> by shifting the poles of
+<math>W </math> by <math> \pm \epsilon </math>, where <math> \epsilon </math> are the poles of the Green's function <math> G</math>.
+Generally, {{TAG|LSPECTRALGW}} affects the compute time very little. QP energies also hardly
+change when {{TAG|LSPECTRALGW}}  is modified.
+However, {{TAG|LSPECTRALGW}} = .TRUE. is usually slightly more robust,
+and should be selected for molecules and other systems with flat dispersion-less bands.
+One the other hand, {{TAG|LSPECTRALGW}} = .TRUE. seems to converge slightly slower,
+as the complex shift {{TAG|CSHIFT}} is decreased. Set this flag, if the QP energies
+show erratic behavior, for instance, if QP energies or Z-factors are not in the expected
+range of values (0.5<Z<0.9).
-A similar trick is used when the QP-shifts are calculated. In general it is strongly recommended to set {{TAG|LSPECTRALGW}} = .TRUE., except if memory requirements are too excessive.
-== Related Tags and Sections ==
+== Related tags and articles ==
-{{TAG|NOMEGA}}
+{{TAG|LSPECTRAL}}
-== Example Calculations using this Tag ==
+{{sc|LSPECTRALGW|Examples|Examples that use this tag}}
 ----
-[[The_VASP_Manual|Contents]]
-[[Category:INCAR]] [[Category:GW]]
+[[Category:INCAR tag]][[Category:Many-body perturbation theory]][[Category:GW]]