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ANTIRES = 0 | 1 | 2 

The flag ANTIRES determines whether the Tamm-Dancoff approximation is used or not. The allowed settings are:

Default: ANTIRES = 0 default: Tamm-Dancoff approximation (TDA)
= 1 yields exact results at ω=1 at roughly the same cost as TDA
= 2 beyond Tamm-Dancoff, coupling between positive and negative frequencies

VASP uses the procedures outlined in Ref. \cite{Sander15} to include contributions beyond Tamm-Dancoff. Beyond TDA calculations increase the computational time and memory requirements by typically a factor of 2.