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# Difference between revisions of "ANTIRES"

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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:

 ANTIRES = 0 ANTIRES = 1 ANTIRES = 2
 Default: ANTIRES = 0 default: Tamm-Dancoff approximation (TDA) = 2 beyond Tamm-Dancoff, coupling between positive and negative frequencies {{{5}}}

\begin{tabular}{ll} {\tt ANTIRES}=0 & default: Tamm-Dancoff approximation (TDA) \\ {\tt ANTIRES}=1 & yields exact results at $\omega=0$ at roughly the same cost as TDA \\ {\tt ANTIRES}=2 & beyond Tamm-Dancoff, coupling between positive and negative frequencies \end{tabular}

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