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Recipe for selfconsistent GW calculations

Selfconsistent GW calculations are only supported in a QP picture. As for GW0, it is possible to update the eigenvalues only (ALGO=GW), or the eigenvalues and one-electron orbitals (ALGO=scGW). In all cases, a quasiparticle picture is maintained, i.e. satellite peaks (shake ups and shake downs) can not be accounted for in the selfconsistency cycle. Selfconsistent GW calculations can be performed by simply repeatedly calling VASP using:

 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05
 ALGO = GW      # eigenvalues only  or alternatively
 ALGO = scGW    # eigenvalues and one electron orbitals
For scGW0 or scGW non diagonal terms in the Hamiltonian are accounted for, e.g. the linearized QP equation is diagonalized, and the one electron orbitals are updated.[114]

Alternatively (and preferably), the user can specify an electronic iteration counter using NELM:

 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05
 ALGO = GW  # or  ALGO = scGW
 NELM = 3
In this case, the one electron energies (=QP energies) are updated 3 times (starting from the DFT eigenvalues) in both G and W. For ALGO = scGW (or ALGO = QPGW in VASP.5.2.13), the one electron energies and one electron orbitals are updated 3 times.[114] As for ALGO = scGW0, the ``static'' COHSEX approximation can be selected by setting NOMEGA = 1 [115]. To improve convergence to the groundstate, the charge density is mixed using a Kerker type mixing starting with VASP.5.2.13 (see Sec. 6.49). The mixing parameters AMIX, BMIX, AMIX_MAG, BMIX_MAG, AMIN can be adjusted, if convergence problems are encountered.

Alternatively the mixing may be switched off by setting IMIX=0 and controlling the step width for the orbitals using the parameter TIME (which defaults to 0.4). This selects a fairly sophisticated damped MD algorithm, that is also used for DFT methods when ALGO is set the ``Damped''. In general, this method is more reliable for metals and materials with strong charge sloshing.


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Next: Caveats for selfconsistent quasiparticle Up: Frequency dependent GW calculations Previous: Recipe for partially selfconsistent   Contents   Index
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