Towards an accurate molecular orbital theory for excited states: Ethene, butadiene, and hexatriene

• DOI: 10.1063/1.465071
• Publication Date: 2002-07-26T12:22:43Z
• Authors: Luis Serrano-Andrés; Manuela Merchán; Ignacio Nebot-Gil; Roland Lindh; Björn O. Roos
• Keywords: Butadiene; Triplets; Errors; Calculation Methods ; Quantum Chemistry ; Ab Initio Calculations ; Electron Spectra ; Butadiene ; Accuracy ; Scf Calculations ; Triplets ; Rydberg States ; Excitation ; Errors ; Polyenes ; Excited States; Scf Calculations; Polyenes; Excited States; Quantum Chemistry; 01 natural sciences; 7. Clean energy; UNESCO::FÍSICA::Química física; 0104 chemical sciences; Electron Spectra; Rydberg States; :FÍSICA::Química física [UNESCO]; Ab Initio Calculations; Accuracy; Excitation; Calculation Methods

A newly proposed quantum chemical approach for ab initio calculations of electronic spectra molecular systems is applied to the molecules ethene, trans-1,3-butadiene, and trans-trans-1,3,5-hexatriene. The method has aim being accurate better than 0.5 eV excitation energies expected provide structural physical data excited states with good reliability. based on complete active space (CAS) SCF method, which gives a proper description major features in structure state, independent its complexity, accounts all near degeneracy effects, includes full orbital relaxation. Remaining dynamic electron correlation effects are subsequent step added using second order perturbation theory CASSCF wave function as reference state. here tested calculation valence Rydberg singlet triplet title molecules, extended atomic natural (ANO) basis sets. ethene comprised two plus 3s, 3p, 3d character, errors computed smaller 0.13 cases except V vertical energy was about 0.4 too large. lowest nine were studied butadiene. largest error (0.37 eV) found 2 1Bu seven hexatriene had less 0.17 eV.