LANCZOSTHR

{TAGDEF|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 sampling

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

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

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Related tag and articles

IBSE, BSEPREC, NBANDSV, NBANDSO, CSHIFT, OMEGAMAX, BSE calculations, Bethe-Salpeter equations