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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 (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 :
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
is not available
for 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.

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** Up:** Frequency dependent GW calculations
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N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at