LANCZOSTHR

LANCZOSTHR = [real]
Default: LANCZOSTHR = $10^{-3}$ 

Description: LANCZOSTHR is used by the BSE Lanczos algorithm to stop the iterative procedure, once the dielectric function has reached numerical convergence.

The difference between the dielectric function at two consecutive iterations, $i$ and $i+1$, is computed as root-mean-square over the frequency grid

$\mathrm{RMS}[\epsilon] = \sqrt{\sum_{j=1}^N\left[\epsilon_{i}(\omega_j)-\epsilon_{i+1}(\omega_j)\right]^2}$

and once $\mathrm{RMS}[\epsilon]<=$LANCZOSTHR the iterative algorithm stops.

Related tag and articles

BSE, BSE calculations, Bethe-Salpeter equations

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