Total full configuration interaction

The symmetry-adapted functions themselves may then be constructed directly from equations (59), (60), and (61). The same procedure can be applied without any difficulty to the other types of ionic configuration. The results show that there are altogether a total of 268 multiplets of which 22 correspond to xAig states. A similar result, of course, would be obtained from MO theory with full configuration interaction.33... 

Table I summarizes the results for Hg. In order to calculate the activation energy the results shown in Table II for the H atom and Hg molecule at the same level of approximation were used. The total energy, of course, improves as the wavefunction is allowed more variation. However, because the cusp in the wavefunction is poorly represented by one or two Gaussians the total energy is still far from the experimental value. In comparison with the Gaussian work of Schwartz and Schaad,i our best total energy, which involves full configuration interaction, is naturally better than their double Gaussian SCF calculation but not as good as their results with larger basis sets.

Figure 3 Bond dissociation potential for hydrogen flumde computed at various levels of theory with the 6-31G basis set (a) total energies and (b) energy differences relative to full configuration interaction (reproduced with permission from Ref. 4)...

In general, for basis sets which are capable of supporting the level of accuracy required in chemical studies, the full configuration interaction problem is computationally intractable. Even when configuration state functions are employed in place of determinants, the total number of terms in the full configuration interaction expansion is prohibitive. The number of configuration state functions is given by Weyl s number... 

The total symmetry of the molecule is D2h, so we cannot have point group degenerate states. The accidentally degenerate states represented above have C2v symmetry. The direct product C2v Cs recovers properly the full symmetry of the system. Depending on the particular excitation and final spin state four states can be generated. In Table 4 we compare the results of Hartree-Fock (HF), configuration interaction with singles and doubles excitations (CI-SD) and the two structure GMS calculations, with the available experimental data. 

Table 5. Parameter calculations from the dynamic ligand field model for vibronic coupling with the totally symmetric vibrational mode Ui, A without (eo = 20 Dq) and B with configuration interaction (Cl) considering full d matrices (all energies in cm" )...

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