Restrictive active space self-consistent field

Restricted active space self-consistent field (RASSCF) scheme, ab initio calculations, P,T-odd interactions, 253-259... 

The selection of configuration state functions to be included in MCSCF calculations is not a trivial task. Two approaches which can reduce the complexity of the problem are the complete active space self-consistent-field (CASSCF) [68] and the restricted active space self-consistent-field (RASSCF) [69] approach. Both are implemented in the Dalton program package [57] and are used in this study. Throughout the paper a CASSCF calculation is denoted by i active gactive RASSCF calculation by For the active spaces of HF, H2O, and CH4... 

As for any full Cl expansion, the CASSCF becomes unmanageably large even for quite small active spaces. A variation of the CASSCF procedure is the Restricted Active Space Self-consistent Field (RASSCF) method. Here the active MOs are further divided into three sections, RASl, RAS2 and RAS3, each having restrictions on the... 

Restricted Active Space Self-Consistent Field Sn2 reaction, 305, 367 —Variational Transition State Theory (VTST), 306... 

Correlation Restricted Active Space Self-Consistent Field (RASSCF) and Multiconfigurational Second-Order Perturbation Theory (CASPT2)... 

Empirical equilibrium coupling constants can be compared as a benchmark with calculated equilibrium coupling constants obtained with various methods. A comparison of these empirical equilibrium constants with calculated equilibrium constants suggested that the restricted-active-space self-consistent field (RASSCF) method is the best approach for calculating the indirect nuclear spin-spin coupling constants of small molecules, and that the second-order polarization propagator approximation (SOPPA) and DFT are similar in performance. 

More precisely, a set of active orbitals and a number of active electrons are defined. All the configurations that can be built by excitations ofthe active electrons among the active orbitals are included into the wavefunction. Other, more flexible approaches for the selection of the conflgurations included in the MSCSF wavefunction exist, such as the Restricted Active Space Self-Consistent Field [23, 24] (RASSCF) and the Occupation Restricted Multiple Active Space (ORMAS) [25] methods. 

Instead of optimization of all the orbitals, only the active orbitals will be varied within the Complete Active Space Self-Consistent Field approximation (CASSCF). In the acronym of this method, the number of active orbitals and active electrons are also provided for the given system. For instance, CASSCF(6,4) denotes the calculations with the expansion including all the possible exchanges of the four electrons within the six active orbitals. The CASSCF approach leads to all possible exchanges in the given active space, and for a moderately sized system, the size of the active spaces can quickly exceed the computational resources. In such a case, the solution can be the Restricted Active Space Self-Consistent Field method (RASSCF), which supplies a way of limiting the size of the active space. 

On the other hand, the Restricted Active Space Self-Consistent Field (RASSCF) method is a more general extension of the CASSCF method. Now, there are three subspaces within the active orbitals RASl (orbitals that are doubly occupied except for a maximum number of holes allowed in this orbital subspace), RAS2 (in these orbitals, all possible occupations are allowed), and RAS3 (orbitals that are unoccupied except for a maximum number of electrons allowed in this subspace). CASSCF calculations can be performed by allowing orbitals only in the RAS2 space. A single reference SDCl wave function is obtained by allowing a maximum of two holes... 

Malmqvist, P.-A., Rendell, A., 8c Roos, B. O. (1990). The restricted active space self-consistent-field method, implemented with a split graph unitary group approach. The Journal of Physical Chemistry, 94, 5477-5482. 

Reaction coordinate, 296, 314, 365, 368 Reaction Path (RP) methods, 390 Reaction surface, 390 Reaction volume, 390 Redundant variables, 34, 327 Relaxation time, in simulations, 380 Renormalized Davidson correction, 137 Resonance, resonance structures, 200 Response, wave function, 242 Restricted Active Space Self-Consistent Field (RASSCF) method, 119 Restricted Hartree-Fock (RHF) method, 70 Restricted Open-shell Hartree-Fock (ROHF) method, 70... 

Malmqvist P-A, Rendell A, Roos BO. The Restricted Active Space Self-Consistent-Field Method, Implemented with a Split Graph Unitary Group Approach. J Phys Chem. 1990 (4). Ma D, Li Manni G, Gagliardi L. The generalized active space concept in multiconfigurational self-consistent field methods. J Chem Phys [Internet]. 2011 Jul 28 [cited 2012 Mar 1] 135(4) 044128. Available from http //www.ncbi.nlm.nih.gov/pubmed/21806111. 

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