Correlation energy triply excited configurations

Usually, SD-CI wavefiinctions recover about 90-95% of the correlation energy, inclusion of triply and quadruply substituted configurations is adequate for many purposes, and inclusion of quintuply and sextuply excited configurations is sufficient for describing most chemical reactions. Since the explosion of the number of configurations typically starts with the quadruple excitations, our first priority is the predictive deletion of deadwood from this group. 

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