Orbitals, amplitude energy

Orbital amplitudes, 54 Orbital energies, 51, 53, 287 Orbital interactions general rules, 10, 38 Orbital labels group theoretical, 46, 51 localized types, 51 Orbital occupancies, 57 Oxygen, 88 Ozone, 151... 

Keywords Chemical orbital theory. Electron delocalization. Frontier orbital. Orbital amplitude, Orbital energy, Orbital interaction. Orbital mixing rule, Orbital phase, Orbital phase continuity, Orbital phase environment. Orbital synunetry, Reactivity, Selectivity... 

Poles and residues of the electron propagator Gv, ( j provide the spin orbital energies and the molecular orbital amplitudes. The sum of the energies of the occupied spin orbitals is used as a measure of the total energy of the 7t-orbital system and Coulson observed that this could be expressed as a contour integral in the complex energy plane... 

The electronic energy W in the Bom-Oppenlieimer approxunation can be written as W= fV(q, p), where q is the vector of nuclear coordinates and the vector p contains the parameters of the electronic wavefimction. The latter are usually orbital coefficients, configuration amplitudes and occasionally nonlinear basis fiinction parameters, e.g., atomic orbital positions and exponents. The electronic coordinates have been integrated out and do not appear in W. Optimizing the electronic parameters leaves a function depending on the nuclear coordinates only, E = (q). We will assume that both W q, p) and (q) and their first derivatives are continuous fimctions of the variables q- and py... 

Onee the requisite one- and two-eleetron integrals are available in the moleeular orbital basis, the multieonfigurational wavefunetion and energy ealeulation ean begin. Eaeh of these methods has its own approaeh to deseribing the eonfigurations Oj ineluded in the ealeulation and how the Cj amplitudes and the total energy E is to be determined. 

Such a compact MCSCF wavefunction is designed to provide a good description of the set of strongly occupied spin-orbitals and of the CI amplitudes for CSFs in which only these spin-orbitals appear. It, of course, provides no information about the spin-orbitals that are not used to form the CSFs on which the MCSCF calculation is based. As a result, the MCSCF energy is invariant to a unitary transformation among these virtual orbitals. 

The effeet of adding in the py orbitals is to polarize the 2s orbital along the y-axis. The amplitudes Cn are determined via the equations of perturbation theory developed below the ehange in the energy of the 2s orbital eaused by the applieation of the field is expressed in terms of the Cn eoeffieients and the (unperturbed) energies of the 2s and npy orbitals. 

The Brueckner-reference method discussed in Section 5.2 and the cc-pvqz basis set without g functions were applied to the vertical ionization energies of ozone [27]. Errors in the results of Table IV lie between 0.07 and 0.17 eV pole strengths (P) displayed beside the ionization energies are approximately equal to 0.9. Examination of cluster amplitudes amd elements of U vectors for each ionization energy reveals the reasons for the success of the present calculations. The cluster operator amplitude for the double excitation to 2bj from la is approximately 0.19. For each final state, the most important operator pertains to an occupied spin-orbital in the reference determinant, but there are significant coefficients for 2h-p operators. For the A2 case, a balanced description of ground state correlation requires inclusion of a 2p-h operator as well. The 2bi orbital s creation or annihilation operator is present in each of the 2h-p and 2p-h operators listed in Table IV. Pole strengths are approximately equal to the square of the principal h operator coefiScient and contributions by other h operators are relatively small. 

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