title: Electron correlation effects and density analysis of the first-order hyperpolarizability of neutral guanine tautomers.
abstract: Dipole moments (μ), charge distributions, and static electronic first-order hyperpolarizabilities (β(μ)) of the two lowest-energy keto tautomers of guanine (7H and 9H) were determined in the gas phase using Hartree-Fock, Møller-Plesset perturbation theory (MP2 and MP4), and DFT (PBE1PBE, B97-1, B3LYP, CAM-B3LYP) methods with Dunning's correlation-consistent aug-cc-pVDZ and d-aug-cc-pVDZ basis sets. The most stable isomer 7H exhibits a μ value smaller than that of the 9H form by a factor of ca. 3.5. The β μ value of the 9H tautomer is strongly dependent on the computational method employed, as it dramatically influences the β(μ) (9H)/β(μ) (7H) ratio, which at the highest correlated MP4/aug-cc-pVDZ level is predicted to be ca. 5. The Coulomb-attenuating hybrid exchange-correlation CAM-B3LYP method is superior to the conventional PBE1PBE, B3LYP, and B97-1 functionals in predicting the β(μ) values. Differences between the largest diagonal hyperpolarizability components were clarified through hyperpolarizability density analyses. Dipole moment and first-order hyperpolarizability are molecular properties that are potentially useful for distinguishing the 7H from the 9H tautomer.
authors.affiliation: Department of Chemistry, University of Catania, viale A. Doria 6, Catania 95125, Italy. agalparone@unict.it
authors.forename: Andrea
authors.initials: A
authors.lastname: Alparone
mesh_terms: D004583:Electrons; D005740:Gases / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D011789:Quantum Theory; D055672:Static Electricity; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D005740:Gases; D006147:Guanine