Multiconfiguration self-consistent field calculations

In the Cl methods mentioned so far, only the mixing coefficients of the excited configurations are optimized in the variational calculations. If we optimize both the coefficients of the configurations and those of the basis functions, the method is called MCSCF, which stands for multiconfiguration self-consistent field calculation. One popular MCSCF technique is the complete active-space... 

K. Ruud, T. Helgaker, R. Kobayashi, P. Jorgensen, K. Bak, H. Jensen, Multiconfigurational self-consistent field calculations of nuclear shieldings using london atomic orbitals, J. Chem. Phys. 100 (1994) 8178. 

A. Hartree-Fock, Configuration-interaction and Multiconfiguration Self-consistent Field Calculations... 

Figure 4.6 Potential energy curves for six electronic states of NaH. The curve labeled "ionic" is the function e / ne R. approaching the energy of Na + H at infinite separation. From multiconfigurational self-consistent field calculations by E. S. Sachs, J. Hinze, and N. H. Sabelli, J. Chem. Phys. 62 3367 (1975) used with permission.

Jensen, H. J. Aa., Jprgensen, R, Agren, H., and Olsen, J. (1988a). Second-order Mpller-Plesset perturbation theory as a configuration and orbital generator in multiconfiguration self-consistent field calculations. J. Chem. Phys., 88, 3834-3839. 

Multiconfiguration self-consistent-field calculations of hyperfine coupling constants. Journal of Chemical Physics, 97, 3412. 

Calculation of rotational and vibrational g factors by linear response methods using multiconfigurational self-consistent-field wave functions is described in detail elsewhere [18,27]. 

Another class of methods uses more than one Slater determinant as the reference wave function. The methods used to describe electron correlation within these calculations are similar in some ways to the methods listed above. These methods include multiconfigurational self-consistent field (MCSCF), multireference single and double configuration interaction (MRDCI), and /V-clcctron valence state perturbation theory (NEVPT) methods.5... 

Nondynamical electron correlation effects are generally important for reaction path calculations, when chemical bonds are broken and new bonds are formed. The multiconfiguration self-consistent field (MCSCF) method provides the appropriate description of these effects [25], In the last decade, the complete active space self-consistent field (CASSCF) method [26] has become the most widely employed MCSCF method. In the CASSCF method, a full configuration interaction (Cl) calculation is performed within a limited orbital space, the so-called active space. Thus all near degeneracy (nondynamical electron correlation) effects and orbital relaxation effects within the active space are treated at the variational level. A full-valence active space CASSCF calculation is expected to yield a qualitatively reliable description of excited-state PE surfaces. For larger systems, however, a full-valence active space CASSCF calculation quickly becomes intractable. 

The adiabatic potential energy curves for these electronic states calculated in the Born-Oppenhelmer approximation, are given in Figure 1. Since we have discussed the choice of basis functions and the choice of configurations for these multiconfiguration self-consistent field (MCSCF) computations (12) previously (] - ), we shall not explore these questions in any detail here. Suffice it to say that the basis set for Li describes the lowest 2s and 2p states of the Li atom at essentially the Hartree-Fock level of accuracy, and includes a set of crudely optimized d functions to accommodate molecular polarization effects. The basis set we employed for calculations involving Na is somewhat less well optimized than is the Li basis in particular, so molecular orbitals are not as well described for Na2 (relatively speaking) as they are for LI2. 

Several theoretical studies of diazirinyl radicals have been undertaken. Multiconfiguration self-consistent field (MCSCF) calculations have been used to investigate the stability of, and isomerization between, the diazirinyl anion 6 and the open-chain biradical anion 7 (Scheme 1) <1995JPC6548>. Dimerization of aryldiazirinyl radicals has been explored by computational and experimental methods <2004PCCP756>. Both approaches support the predominance of the N-N dimer 9 over the isomeric C-N form 8. Furthermore, bimolecular dimer decomposition was shown to be considerably more favorable than the alternative unimolecular pathways. 

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