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Caveats for selfconsistent quasiparticle GW calculations

Fully selfconsistent calculations with an update of the orbitals in G and W[114] require significant care and are prone to diverge (scGW0 calculations are usually less critical). As discussed in section 6.73.14, one can select this mode using:

 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05
 ALGO = scGW    # eigenvalues and one electron orbitals
 NELM  = number of steps
However, one caveat applies to this case: when the orbitals are update, the derivatives of the orbitals with respect to $ k$ (WAVEDER file) will become incompatible with the orbitals. This can cause severe problems and convergence to the incorrect solution. For metals, we recommend to avoid using the WAVEDER file alltogether (LOPTICS =.TRUE. should not be used in the preparatory DFT runs). For insulators, VASP (version 5.3.1 or higher) can update the WAVEDER file in each electronic iteration if the finite difference method is used to calculate the first derivative of the orbitals with respect to $ k$:
 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05
 ALGO = scGW    # eigenvalues and one electron orbitals
 NELM  = 10
 LOPTICS = .TRUE. ; LPEAD = .TRUE.
The combination LOPTICS = .TRUE. ; LPEAD = .TRUE. is required since $ \frac{\partial (H - \epsilon_{nk} S)}{\partial k_i}$ is not available for $ GW$ like methods. LPEAD=.TRUE. circumvents this problems (see Sec. 6.67.5) by calculating the derivatives of the orbitals using numerical differentiation on the finite k-point grid (this option is presently limited to insulators).

Vertex corrections are presently not documented. This is a feature still under construction, and we recommend to collaborate with the Vienna group if you are desperately in need for that feature.


next up previous contents index
Next: Using the GW routines Up: Frequency dependent GW calculations Previous: Recipe for selfconsistent GW   Contents   Index
N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at