UPPER AND LOWER BOUNDS TO THE OVERLAP BETWEEN APPROXIMATE AND TRUE WAVEFUNCTIONS
Creators:Alexander, Millard H.
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Publisher:Ohio State University
The determination of upper and lower bounds to the overlap between an approximate wavefunction for a particular atomic or molecular system and the unknown true wavefunction is of interest both as a test of the goodness of the approximate wavefunction and as an essential prerequisite in the determination of error bounds to expectation values. Previous expressions for bounds to the overlap may require the computation of difficult matrix elements and often yield bounds of poor quality. We present a new extrapolation method which requires only the approximately mate wavefunction, a limited CI wavefunction, and the knowledge of the true energy to obtain bounds to the overlap which are accurate to second order in the expansion of the appropriate secular determinant. The method is conceptually simple and when applied to actual systems yields tight bounds of high accuracy.
Author Institution: Department of Chemistry, Harvard University