CI size consistency and separated fragments
Research context
postgraduate concept · conditional · As of 2026-10-10
Truncated CI can retain a variational upper bound yet fail size consistency because products of fragment excitations may lie outside its excitation space.
Key knowledge
Truncated CI can retain a variational upper bound yet fail size consistency because products of fragment excitations may lie outside its excitation space. A separated-fragment test therefore probes a different property from variationality.
Conditions and scope
- Use noninteracting fragments with consistent Hamiltonian/reference conventions; active-space omissions remain even if a CI calculation converges.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Configuration Interaction Theory: Variational theorem (pp. 17–20); size consistency/extensivity (pp. 31–33) (extracted lecture-note sections)
2026-10-10 · Bounded author source inspection of ci size consistency and separated fragments, including the stated conditions; independent branch review is recorded separately.
Entry details
Permanent link to this entry ↗- Record identity
- res-chem-truncated-ci
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference