Electronic excitation energies of pyrimidine studied using coupled cluster response theory

VUV photophysics and dissociative photoionization of pyrimidine, purine, imidazole and benzimidazole in the 7–18eV photon energy range

“…These result in Franck-Condon transition shifts, as confirmed by theoretical calculations on the nucleobases, discussed elsewhere [5]. The vertical and adiabatic (0-0) ionization energies of pyrimidine have been calculated using coupled cluster response theory and unrestricted DFT B3LYP/cc-pVDZ [43], giving a difference of 490 meV, in excellent agreement with our measurements. In pyrimidine, Potts et al [24] agree with Gleiter et al [41], as well as Asbrink et al [42] and Piancastelli et al [39], that ionization, which involves removal of an electron from the 7b 2 molecular orbital, concerns a non-bonding nr orbital on nitrogen.…”

Basis set effects on coupled cluster benchmarks of electronically excited states: CC3, CCSDR(3) and CC2

“…Refs. [11][12][13][14][15]). However, even the aug-cc-pVTZ basis set is not optimal for Rydberg states in general, and hence additional molecule-centered diffuse basis functions may be necessary for an accurate description of states with significant valence-Rydberg mixing.…”

Excited state coupled cluster methods

“…For example, the band may be broad and, more appropriately, described as an interval of strong absorption and without a clear maximum. 66,67 Often, it is only a few of the vibrational modes that actively contribute to the absorption profile. In contrast, all modes contribute to the difference in zero-point vibrational energy.…”