Quadratic configuration-interaction theory

QCISD, QCISDT quadratic configurational interaction theory... 

Z. He and D. Cremer, Int. J. Quantum Chem., Quant. Chem. Symp., 25,43 (1991). Analysis of Coupled Cluster and Quadratic Configuration Interaction Theory in Terms of Sixth-Order Perturbation Theory. Z. He and D. Cremer, Theor. Chim. Acta, 85, 305 (1993). Analysis of Coupled Cluster Methods. 11. What Is the Best Way to Account for Triple Excitation in Coupled Cluster Theory. ... 

Z. He and D. Cremer, Int. J. Quantum Chem., Quantum Chem. Symp, 25, 43 (1991). Analysis of Coupled Cluster and Quadratic Configuration Interaction Theory in Terms of Sixth-Order Perturbation Theory. 

Curtiss, L. A. Raghavachari, K. Pople, J. A. Gaussian-2 theory use of higher level correlation methods, quadratic configuration interaction geometries, and second-order Mpller Plesset zero-point energies. J. Chem. Phys. 1995, 103, 4192-4120. 

Scott, A. P., Radom, L., 1996, Harmonic Vibrational Frequencies An Evaluation of Hartree-Fock, Moller-Plesset, Quadratic Configuration Interaction, Density Functional Theory, and Semiempirical Scale Factors , J. Phys. Chem., 100, 16502. 

There is also a hierarchy of electron correlation procedures. The Hartree-Fock (HF) approximation neglects correlation of electrons with antiparallel spins. Increasing levels of accuracy of electron correlation treatment are achieved by Mpller-Plesset perturbation theory truncated at the second (MP2), third (MP3), or fourth (MP4) order. Further inclusion of electron correlation is achieved by methods such as quadratic configuration interaction with single, double, and (perturbatively calculated) triple excitations [QCISD(T)], and by the analogous coupled cluster theory [CCSD(T)] [8],... 

Scott AP, Radom L(1996) Harmonic vibrational frequencies An evaluation of Hartree-Fock, Moller-Plesset, quadratic configuration interaction, density functional theory, and semiempirical scale factors. J Phys Chem 100 16502-16513... 

L. A. Curtiss, K. Raghavachari, and J. A. Pople, /. Chem. Phys., 103, 4192 (1995). Gaus-sian-2 Theory Use of Higher Level Correlation Methods, Quadratic Configuration Interaction Geometries, and Second-Order Moller-Plesset Zero-Point Energies. 

Pending ongoing developments of improved functionals, an effective multi-scale scheme (sketched in Figure 2.3) can be profitably used, where the NO moiety is treated at the Quadratic Configuration Interaction Single and Double (QCISD) level of theory and the remaining parts of the system are treated by means of hybrid density functionals ... 

Rico RJ, Lee TJ, Head-Gordon M (1994) The origin of differences between coupled cluster theory and quadratic configuration interaction for excited states. Chem Phys Lett 218 139-146. 

Scott, A. R Radom, L. Harmonic vibrational frequencies an evaluation of Hartree-Fock, Moller-Plesset, quadratic configuration interaction, density functional theory, and semiempirical scale factors, J. Phys. Chem. 1996,100, 16502-16513. Halls, M. D. VeUcovski, J. Schlegel, H. B. Harmonic frequency scaling factors for Hartree-Fock, S-VWN, B-LYP, B3-LYP, B3-PW91 and MP2 with the Sadlej pVTZ electric property basis set, Theor. Chem. Acc. 2001,105, 413-421. 

Restrepo-Cossio, A. A., Gonzalez, C. A., Mari, F. Comparative ab Initio Treatment (Hartree-Fock, Density Functional Theory, MP2, and Quadratic Configuration Interactions) of the Cycloaddition of Phosphorus Ylides with Formaldehyde in the Gas Phase. J. Phys. Chem. A 1998, 102, 6993-7000. 

Accounting for relativistic effects in computational organotin studies becomes complicated, because Hartree-Fock (HF), density functional theory (DFT), and post-HF methods such as n-th order Mpller-Plesset perturbation (MPn), coupled cluster (CC), and quadratic configuration interaction (QCI) methods are non-relativistic. Relativistic effects can be incorporated in quantum chemical methods with Dirac-Hartree-Fock theory, which is based on the four-component Dirac equation. " Unformnately the four-component Flamiltonian in the all-electron relativistic Dirac-Fock method makes calculations time consuming, with calculations becoming 100 times more expensive. The four-component Dirac equation can be approximated by a two-component form, as seen in the Douglas-Kroll (DK) Hamiltonian or by the zero-order regular approximation To address the electron cor-... 

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