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# LSPECTRALGW

If LSPECTRALGW = .TRUE. is set, the imaginary part of the self-energy ${\displaystyle \Sigma (\omega )=GW}$ is calculated from the imaginary part of screened potential ${\displaystyle W(\omega )}$ by shifting the poles of ${\displaystyle W}$ by ${\displaystyle \pm \epsilon }$ , where ${\displaystyle \epsilon }$ are the poles of the Green's function ${\displaystyle G}$ . 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).