LSPECTRALGW

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).

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