Coupled-cluster truncation and virtual-space error
Research context
postgraduate concept · conditional · As of 2026-10-10
CCSD and perturbative-triples CCSD(T) truncate correlation differently from CI; FNO variants also truncate the virtual space using MP2-derived occupations.
Key knowledge
CCSD and perturbative-triples CCSD(T) truncate correlation differently from CI; FNO variants also truncate the virtual space using MP2-derived occupations. Threshold and basis convergence must be tested against the property of interest, especially when the single-reference picture is questionable.
Conditions and scope
- A computed coupled-cluster energy is not a variational bound; MP2 virtual-space selection can be inadequate for strongly correlated cases.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
FNOCC: density-fitted coupled-cluster methods: CCSD/CCSD(T), virtual natural-orbital truncation and MP2 correction (relevant full-text sections); 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 coupled-cluster truncation and virtual-space error, including the stated conditions; independent branch review is recorded separately.
Entry details
Permanent link to this entry ↗- Record identity
- res-chem-coupled-cluster
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference