Fock space multi-reference coupled-cluster study of excitation energies and dipole oscillator strengths of ozone

Quasiparticle Fock-space coupled-cluster theory

“…(70), but looks very similar to the untransformed form of Eq. (32). At this point the classical approach and the present one enter the diverging paths.…”

“…The operators that commute with the particle-number operator (30) are called the electron-number conserving operators; Hamiltonian (32) belongs to this class. This gives rise to an important continuous symmetry ofĤ, governed by a unitary group U (1) (in one dimension).…”

“…The necessary formulas can be derived by using the diagrammatic language employed in the derivation of the CC equations (110), (111), and (112). Applications of this approach may be found in the papers by Barysz et al [32,33].…”

Excited and ionized states of ozone studied by the MEG (multi-exponentially generated)/EX (excited)-MEG method

“…Hartree-Fock (HF) single determinant becomes inadequate approximation due to the quasidegenerate electronic structure. Therefore, ozone has been a benchmark molecule [4][5][6][7][8][9][10][11] in the methodological developments of the multi-reference type theories in modern quantum chemistry.…”

“…Ionization spectra of ozone have also been extensively studied both by experiments [12][13][14][15][16][17][18] and theories [4,6,9,[19][20][21][22][23][24][25][26][27]. The quasi-degeneracy in the ground state causes a breakdown of the Koopmans' picture.…”