Configuration interaction description

Davidson, E. R. Configuration Interaction description of electron correlation, in The World of Quantum Chemistry, ed. Daudel, R. and Pullman, B. D. Reidel, Dordrecht 1974. 

Reidel, Dordrecht, 1974, pp. 17—30. Configuration Interaction Description of Electron Correlation. 

We discuss the situation pertaining to a simple octahedral complex of a M transition metal ion [e.g., MF orMO ). The details have been given many times previously e.g., Refs. (77, 26, 30, 31). Bonding is assumed to place between the metal ion and the ligand ions. The relation of the MO formalism to the configuration interaction description has been discussed by Owen and Thornley (77). 

D. Beljonne, F. Meyers, J. L. Br6das, Excited states in bis-substituted polyenes configuration interaction description of the vertical excitation energies and nonlinear optical properties, Synth. Met., 80, 211-222 (1996). 

Orbit Coupling and Intersystem Crossing in Conjugated Polymers A Configuration Interaction Description. 

E. R. Davidson, in The World of Quantum Chemistry, R. Dandel and B. Pullman, Eds., Reidel, Dordrecht, 1974, pp. 17-30. Configuration Interaction Description of Electron Correlation. 

Fink RF et al (2008) Ab initio configuration interaction description of excitation energy transfer between closely packed molecules. Chem Phys 343 353-361... 

A CASSCF calculation is a combination of an SCF computation with a full Configuration Interaction calculation involving a subset of the orbitals. The orbitals involved in the Cl are known as the active space. In this way, the CASSCF method optimizes the orbitals appropriately for the excited state. In contrast, the Cl-Singles method uses SCF orbitals for the excited state. Since Hartree-Fock orbitals are biased toward the ground state, a CASSCF description of the excited state electronic configuration is often an improvement. 

The description of configuration interaction given for rr-electron methods is also valid for all-valence-electron methods. Recently, two papers were published in which the half-electron method was combined with a modified CNDO method (69) and the MINDO/2 method was combined with the Roothaan method (70). Appropriate semiempirical parameters and applications of all-valence-electron methods are most probably the same as those reviewed for closed-shell systems (71). 

A description as a MMCT transition is not very obvious for this case. However, there is no essential difference between the physical origin of the colors of Pb(N02)2 and, for example, CU2WO4. Unfortunately the literature shows sometimes discussions on the nature of their excited states in terms of either MMCT or metal-ion-induced CT transitions. To us, such a discussion does not seem to be very fruitful. In the classification it is a matter of taste which nomenclature is used, in the (more difficult) characterization it is essential to determine the coefficients which indicate the amount of configuration interaction. The latter describe the nature of the excited state. 

Cl methods [21] add a certain number of excited Slater determinants, usually selected by the excitation type (e.g. single, double, triple excitations), which were initially not present in the CASSCF wave function, and treat them in a non-perturbative way. Inclusion of additional configurations allows for more degrees of freedom in the total wave function, thus improving its overall description. These methods are extremely costly and therefore, are only applicable to small systems. Among this class of methods, DDCI (difference-dedicated configuration interaction) [22] and CISD (single- and double excitations) [21] are the most popular. 

In this chapter, we will study the elementary reaction steps of these mechanisms focusing primarily on the anthraphos systems. This chapter begins with a description of the impact of different methods (coupled cluster, configuration interaction and various DFT functionals), different basis sets, and phosphine substituents on the oxidative addition of methane to a related Ir system, [CpIr(III)(PH3)Me]+. Then, it compares the elementary reaction steps, including the effect of reaction conditions such as temperature, hydrogen pressure, alkane and alkene concentration, phosphine substituents and alternative metals (Rh). Finally, it considers how these elementary steps constitute the reaction mechanisms. Additional computational details are provided at the end of the chapter. 

The theoretical description based on the lattice or cell models of the liquid uses the language contributing states of occupancy . Nevertheless, these states ot occupancy are not taken to be real, and the models are, fundamentally, of the continuum type. The contribution to the free energy function of different states of occupancy of the basic lattice section is analogous to the contribution to the energy of a quantum mechanical system of terms in a configuration interaction series. 

If we choose only one determinant built from the lowest /2 SCF-orbitals, the "configuration interaction method will naturally give us Wq = Ao with the energy eigenvalue q as the best groimd-state description. This is clearly identical with the SCF result of the last section. 

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