Multiconfiguration self-consistent field dynamics

It is possible to divide electron correlation as dynamic and nondynamic correlations. Dynamic correlation is associated with instant correlation between electrons occupying the same spatial orbitals and the nondynamic correlation is associated with the electrons avoiding each other by occupying different spatial orbitals. Thus, the ground state electronic wave function cannot be described with a single Slater determinant (Figure 3.3) and multiconfiguration self-consistent field (MCSCF) procedures are necessary to include dynamic electron correlation. 

C. Woywod, W. Domcke, A. L. Sobolewski, and H-J Werner, Characterization of the 5,-5 conical intersection in pyrazine using ab initio multiconfiguration self-consistent-field and multireference configuration-interaction methods, J. Chem. Phys. 100 1400 (1994) G Stock and W. Domcke, Femtosecond spectroscopy of ultrafast nonadiabatic excited-state dynamics on the basis of ab initio potential-energy surfaces the S2 state of pyrazine, J. Phys. Chem. 97 12466 (1993). 

AIMD = ab initio molecular dynamics B-LYP = Becke-Lee-Yang-Parr CCSD = coupled cluster single double excitations CVC = core-valence correlation ECP = effective core potential DF = density functional GDA = gradient corrected density approximation MCLR = multiconfigurational linear response MP2 = M0ller-Plesset second-order (MRD)CI = multi-reference double-excitation configuration interaction RPA = random phase approximation TD-MCSCF = time-dependent multiconfigurational self-consistent field TD-SCF = time-dependent self-consistent field. 

In this chapter, the quantum chemical simulation of actinide and lanthanide complexes will be considered. The need for a multiconfigurational description of the wavefimction is discussed, and the complete-active-space self-consistent-field (CASSCF) approach, along with some related methods, is introduced and discussed. This approach, originally developed by Bj om Roos, allows for the strong static correlation present in these complexes due to a combination of electron-electron interactions and weak crystal field splittings to be taken into consideration in a systematic manner. Extensions to this approach, which also account for dynamical correlation will also be considered, fit the finally section, the application of the CASSCF approach will be illustrated with examples from the literature. 

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