# Quadratic configuration interaction

- Quadratic configuration interaction
**Quadratic configuration interaction** is an extension of Configuration interaction that corrects for size-consistency errors in the all singles and double excitation CI methods (CISD).Size-consistency means that the energy of two non-interacting (i.e. at large distance apart) molecules calculated directly will be the sum of the energies of the two molecules calculated separately. This method called QCISD was developed in the group of John Pople. It gives results that are comparable to the Coupled cluster method CCSD. QCISD can be improved by the same perturbative inclusion of unlinked triples to give QCISD(T). This gives similar results to CCSD(T).

**References**

Pople, J. A., Head-Gordon, M. and Raghavachari, K. "Journal of Chemical Physics", **87**, 5968, (1987).

*Wikimedia Foundation.
2010.*

### Look at other dictionaries:

**Configuration interaction** — Electronic structure methods Tight binding Nearly free electron model Hartree–Fock method Modern valence bond Generalized valence bond Møller–Plesset perturbation theory … Wikipedia

**Ab initio quantum chemistry methods** — are computational chemistry methods based on quantum chemistry.[1] The term ab initio was first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene.[2][3] The… … Wikipedia

**Post-Hartree-Fock** — In computational chemistry, Post Hartree Fock methods are the set of methods developed to improve on the Hartree Fock (HF), or self consistent field (SCF) method. They add electron correlation which is a more accurate way of including the… … Wikipedia

**Size consistency** — In quantum chemistry, size consistency (or strict separability) is a property that guarantees the consistency of the energy behavior when interaction between the involved molecular system is nullified (for example, by distance). Let A and B be… … Wikipedia

**Hartree-Fock** — In computational physics and computational chemistry, the Hartree Fock (HF) method is an approximate method for the determination of the ground state wavefunction and ground state energy of a quantum many body system.The Hartree Fock method… … Wikipedia

**Quantum chemistry composite methods** — are ab initio post Hartree Fock methods in computational chemistry that aim for high accuracy by combining the results of several calculations. They combine methods with a high level of theory and a small basis set with methods that employ lower… … Wikipedia

**QCI** — Queen Charlotte Islands (Regional) * Quality Council of India (Governmental) * Quadratic Configuration Interaction (Academic & Science » Physics) * Quality Conformance Inspections (Governmental » Military) * Quality Computing, Inc. (Business »… … Abbreviations dictionary

**QCI** — abbr. Quadratic Configuration Interaction … Dictionary of abbreviations

**COLUMBUS** — is a computational chemistry software suite for calculating ab initio molecular electronic structures, designed as a collection of individual programs communicating through files. The programs focus on extended multi reference calculations of… … Wikipedia

**Резонанс Фано** — тип резонанса с асимметричным профилем, возникающего в результате интерференции двух волновых процессов. Природа интерферирующих процессов может быть самой различной, поэтому такой резонанс носит универсальный характер и появляется в различных… … Википедия