Complete active space self-consistent-field CASSCF wave function

The complete active space valence bond (CASVB) method is an approach for interpreting complete active space self-consistent field (CASSCF) wave functions by means of valence bond resonance structures built on atom-like localized orbitals. The transformation from CASSCF to CASVB wave functions does not change the variational space, and thus it is done without loss of information on the total energy and wave function. In the present article, some applications of the CASVB method to chemical reactions are reviewed following a brief introduction to this method unimolecular dissociation reaction of formaldehyde, H2CO — H2+CO, and hydrogen exchange reactions, H2+X — H+HX (X=F, Cl, Br, and I). 

Multireference configuration interaction (MRCI) calculations based on valence complete active space self-consistent field (CASSCF) wave functions with the quadruples corrections (-I-Q) [25-30] were used to determine the excitation energies of the N and P atoms using the AVQZ basis set. 

Density functional theory, direct molecular dynamics, complete active space self-consistent field (CASSCF) technique, non-adiabatic systems, 404-411 Density operator, direct molecular dynamics, adiabatic systems, 375-377 Derivative couplings conical intersections, 569-570 direct molecular dynamics, vibronic coupling, conical intersections, 386-389 Determinantal wave function, electron nuclear dynamics (END), molecular systems, final-state analysis, 342-349 Diabatic representation ... 

The wave function of fragment A, ll a, can either be a single determinant from HF theory or Kohn-Sham DFT, or a multiconfiguration wave function derived from complete active space self-consistent field (CASSCF) or valence bond (VB) calculations. 

ACES II Anharmonic Molecular Force Fields Bench-mark Studies on Small Molecules Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Configuration Interaction Core-Valence Correlation Effects Coupled-cluster Theory Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field G2 Theory Heats of Formation Hybrid Methods Hydrogen Bonding 1 M0ller-Plesset Perturbation Theory NMR Data Correlation with Chemical Structure Photochemistry Proton Affinities r 2 Dependent Wave-functions Rates of Chemical Reactions Reaction Path Following Reaction Path Hamiltonian and its Use for Investigating Reaction Mechanisms Spectroscopy Computational... 

Extended articles on the most common electron correlation methods such as limited configuration interaction (Cl see Configuration Interaction), M0ller-Plesset many-body perturbation theory (MBPT see M0ller Plesset Perturbation Theory), variation-perturbation methods (such as PCILO see Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) and Configuration Interaction), and coupled cluster theory (CC see Coupled-cluster Theory), as well as on explicitly ri2-dependent wave functions (see rxi Dependent Wave functions), can be found elsewhere. 

This calculation is typically performed in some form of a restricted configuration interaction (Cl) expansion (CASSCF [complete active space self consistent field], MRCI [multireference configuration interaction]). The perturbation V is represented by the operators and The perturbed wave function F and energy E satisfy the equation... 

Roos, B. O., The complete active space self-consistent-field method and its applications in electronic structure calculations. Adv. Chem. Phys. 69 399 (1987). One of the most successful methods for finding highly accurate wave functions. CASSCF is a variant of MCSCF and uses all the tricks of the trade (direct Cl, unitary group approach, etc.) in its implementation. 

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