Configuration-interaction theory dissociation

The shape resonances have been described by Feshbach in elastic scattering cross-section for the processes of neutron capture and nuclear fission [7] in the cloudy crystal ball model of nuclear reactions. These scattering theory is dealing with configuration interaction in multi-channel processes involving states with different spatial locations. Therefore these resonances can be called also Feshbach shape resonances. These resonances are a clear well established manifestation of the non locality of quantum mechanics and appear in many fields of physics and chemistry [8,192] such as the molecular association and dissociation processes. 

Other recent papers on the role of negative ions in collisional processes that supplement the treatment of Chen are those by Bardsley [145], which discuss the theory of configuration interaction in relation to molecular states that have sufficient energy to decay by electron emission (or predissociation) and the theory of dissociative recombination. 

The MO function (13.108) underestimates electron correlation, in that it says that structures with both electrons on the same atom are just as likely as structures with each electron on a different atom. The VB function (13.109) overestimates electron correlation, in that it has no contribution from structures with both electrons on the same atom. In MO theory, electron correlation can be introduced by configuration interaction. In VB theory, electron correlation is reduced by ionic-covalent resonance. The simple VB method is more reliable at large R than the simple MO method, since the latter predicts the wrong dissociation products. 

Figure 1 Bond dissociation potential for H2 computed with RHF, UHF, PUHF (projected UHF), RMP2 (restricted MP2), UMP2 (unrestricted MP2), PMP2 (projected MP2), and full configuration interaction levels of theories using a minimal basis set. Typical RHF and UHF orbitals are shown in the insets the UHF bonding orbitals can be written as a linear combination of the RHF bonding and antibonding orbitals (equation 3) (adapted with permission from Ref. 12)...

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)...

Figure 4. Double bond dissociation of the water molecule using the perfect pairing (PP), imperfect pairing (IP) and restricted pairing (GVB-RCC) local correlation models, compared to full configuration interaction (FCI) and Hartree-Fock theory in a minimal (STO-3G) basis.

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