Two configuration self consistent field

Slater Type Orbital using 3 primitive Gaussians Two Configuration Self-Consistent Field Thermal Desorption Study... 

They showed that the dimerized bond should be considered as a singlet diradical. Therefore, a qualitatively correct description of the dimer requires at least a generalized valence bond, GVB-PP132, or a two configuration self-consistent field (TCSCF)33 wave function. More recently, Paulus29 performed a more exhaustive multi-reference analysis of silicon clusters and reconfirmed this conclusion. 

Cnrrelafion tSACl models 169 Spinors, 213 Two Configuration Self-consistent Field reactions, 356, 363... 

T. J. Lee, W. D. Allen, and H. F. Schaefer, III, J. Chem. Phys., 87, 7063 (1987). The Analytic Evaluation of Energy First Derivatives for Two-Configuration Self-Consistent Field Configuration Interaction Wavefunctions. Applications to Ozone and Ethylene. 

Fig. 6 Full state curves and reference state curves for H-H and F-F bonds. The MO-generated curves Involve two-configuration self-consistent field (TCSCF) wave functions and reference two-configuration (RTC) states, while the VB curves are covalent and full covalent-ionic state curves (a) and (b) show the dissociation curves for H-H. (c) and (d) show the corresponding curves for F-F. The arrow for F-F shows the magnitude of the REqs as the difference between the reference state (covalent or RTC) and the full state curve. Reproduced with ACS permission from [14]...

The accurate calculation of these molecular properties requires the use of ab initio methods, which have increased enormously in accuracy and efficiency in the last three decades. Ab initio methods have developed in two directions first, the level of approximation has become increasingly sophisticated and, hence, accurate. The earliest ab initio calculations used the Hartree-Fock/self-consistent field (HF/SCF) methodology, which is the simplest to implement. Subsequently, such methods as Mpller-Plesset perturbation theory, multi-configuration self-consistent field theory (MCSCF) and coupled-cluster (CC) theory have been developed and implemented. Relatively recently, density functional theory (DFT) has become the method of choice since it yields an accuracy much greater than that of HF/SCF while requiring relatively little additional computational effort. 

We have seen that the quantum trajectory approach (as does the single configuration self-consistent field approach) leads to equations of motion where one degree of freedom feels the average interaction through an Ehrenfest type average (see, e.g., equations 29, 33, 34, and 51). Thus the interaction or the correlation between the two modes is described approximately. In the limit of narrow wavepackets a term such as the one appearing in equation (51) would approach the classical expression. Assume for instance an exponential interaction potential such that V(r, R) = C exp(—a(R - Xr)), then... 

Glembotskii, I. I., Kibartas, V. V., and Iutsis, A. P., Soviet Phys. 2, 476, Fock self-consistent field for the neutral boron atom in the two configuration approximation."... 

This is possible within the framework of the self-consistent field (SCF) approach to polymer configurations, described more completely elsewhere [18, 19, 51, 52]. Implementation of this method in its full form invariably requires numerical computations which are done in one of two equivalent ways (1) as solutions to diffusion- or Schrodinger-type equations for the polymer configuration subject to the SCF (in which solutions to the continuous-space formulation of the equations are obtained by discretization) or (2) as solutions to matrix equations resulting from a discrete-space formulation of the problem on a lattice. 

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... 

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