Exploring New Construction Schemes for Extended-Hierarchy Configuration–Interaction Wave Functions

systems, NSD and HCH recover static correlation more rapidly in the dissociation regime, whereas VCH remains inefficient across all determinant counts. The present results, obtained in the STO-6G basis for small benchmark systems, are intended as a controlled methodological study of determinant ordering strategies rather than a comprehensive performance assessment. The ehCI framework provides a practical way to analyze how excitation and seniority interact and to design compact CI expansions.