ODDONLYGW

ODDONLYGW = [logical]
Default: ODDONLYGW = .FALSE.

Description: ODDONLYGW allows to avoid the inclusion of the $\Gamma$ point in the evaluation of response functions (in GW calculations).

The independent particle polarizability $\chi_{{\mathbf{q}}}^0 ({\mathbf{G}}, {\mathbf{G}}', \omega)$ is given by:

${\displaystyle \chi_{{\mathbf{q}}}^0 ({\mathbf{G}}, {\mathbf{G}}', \omega) = \frac{1}{\Omega} \sum_{n,n',{\mathbf{k}}}2 w_{{\mathbf{k}}} (f_{n'{\mathbf{k}}+{\mathbf{q}}} - f_{n{\mathbf{k}}}) \times \frac{\langle \psi_{n{\mathbf{k}}}| e^{-i ({\mathbf{q}}+{\mathbf{G}}){\mathbf{r}}} | \psi_{n'{\mathbf{k}}+{\mathbf{q}}}\rangle \langle \psi_{n'{\mathbf{k}}+{\mathbf{q}}}| e^{i ({\mathbf{q}}+{\mathbf{G}}'){\mathbf{r'}}} | \psi_{n{\mathbf{k}}}\rangle} { \epsilon_{n'{\mathbf{k}}+{\mathbf{q}}}-\epsilon_{n{\mathbf{k}}} - \omega - i \eta } }$

If the $\Gamma$ point is included in the summation over $\mathbf{k}$ , convergence is very slow for some materials (e.g. GaAs).

To deal with this problem the flag ODDONLYGW has been included. In the automatic mode, the $\mathbf{k}$ -grid is given by (see Sec. \ref{sec:autok}):

 $\vec{k} = \vec{b}_{1} \frac{n_{1}}{N_{1}} + \vec{b}_{2} \frac{n_{2}}{N_{2}}  + \vec{b}_{3} \frac{n_{3}}{N_{3}} ,\qquad  n_1=0...,N_1-1 \quad  n_2=0...,N_2-1 \quad  n_3=0...,N_3-1.$

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