Electron correlation effects and density analysis of the first-order hyperpolarizability of neutral guanine tautomers

Hyper-Rayleigh scattering of adenine, thymine, and cytosine in neat water

The first hyperpolarizabilities of the DNA bases thymine and cytosine were determined by hyper-Rayleigh scattering in neat water despite their low solubility. Due to the low intensity levels collected, count statistics were performed instead of the standard dilution procedure. The first hyperpolarizabilities were found to be β_Thymine = (2.99 ± 0.44) × 10^-30 esu for thymine and β_Cytosine = (3.35 ± 0.21) × 10^-30 esu for cytosine. Due to its weak solubility, only an upper limit β_Adenine < (1.82 ± 0.10) × 10^-30 esu could be set for adenine. The first hyperpolarizability of guanine could not be measured because of its very weak solubility. Theoretical static and 800 nm dynamic first hyperpolarizability tensor elements were also computed with Gaussian 09 for comparison.

Electronic responses of long chains to electrostatic fields: Hartree-Fock vs. density-functional theory: a model study

The response to an electrostatic field is determined through simple model calculations, within both the restricted Hartree-Fock and density functional theory methods, for long, finite as well as infinite, periodic chains. The permanent dipole moment, μ0, the polarizability, α, and the hyperpolarizabilities β and γ, calculated using a finite-field approach, are extensively analyzed. Our simple model allows for treatment of large systems and for separation of the properties into atomic and unit-cell contributions. That part of the response properties attributable to the terminations of the finite system change into delocalized current contributions in the corresponding infinite periodic system. Special emphasis is placed on analyzing the reasons behind the dramatic overestimation of the response properties found with density functional theory methods presently in common use.

Solvation effects on the static and dynamic first-order electronic and vibrational hyperpolarizabilities of uracil: a polarized continuum model investigation

Electronic (β(e)) and vibrational (β(v)) first-order hyperpolarizabilities of uracil were determined in gas and water solution using the Coulomb-attenuating Density Functional Theory level with the Dunning's correlation-consistent aug-cc-pVDZ basis set. Frequency-dependent β(e) values were computed for the Second Harmonic Generation (SHG) and Electric Optical Pockels Effect (EOPE) nonlinear optical phenomena. The Polarized Continuum Model was employed to study the solvent effects on the electronic and vibrational properties. The introduction of solvation contributions increases the β(e) (static) value by ca. 110%. In comparison, smaller enhancements are found for the β(e) (EOPE) and β(e) (SHG) data evaluated at the typical wavelength of 694 nm (by 40-50%). The gas-water hyperpolarizability difference was rationalised through a density analysis study. The magnitudes of the vibrational first-order hyperpolarizabilities are comparable to their electronic counterparts and noticeably increase in solution: β(v) (EOPE) ~ β(e) (EOPE) in aqueous phase at λ = 694 nm. Analysis of the IR and Raman spectra is useful to elucidate the most important contributing modes to the vibrational first-order hyperpolarizabilities.

Static and dynamic electronic (hyper)polarizabilities of dimethylnaphthalene isomers: characterization of spatial contributions by density analysis

Static and frequency-dependent electronic (hyper)polarizabilities of the dimethylnaphthalene (DMN) isomers were computed in vacuum using the Coulomb-attenuating Density Functional Theory method. The nonlinear optical Second Harmonic Generation (SHG) and Electro-Optical Pockels Effect (EOPE) were investigated at the characteristic Nd:YAG laser wavelength of 1064 nm. The response electric properties especially the longitudinal polarizability, polarizability anisotropy, and first-order hyperpolarizability are significantly affected by the position of the methyl groups. The SHG and EOPE techniques can be potentially useful to discriminate the α,α-DMN isomers (2,6-DMN < 2,7-DMN < 2,3-DMN) as well as the β,β-DMN isomers (1,5-DMN < 1,4-DMN < 1,8-DMN). The (hyper)polarizability differences among the investigated DMNs were elucidated through density analysis calculations. The predicted polarizabilities exhibit good linear relationships with the experimental first-order biomass-normalized rate coefficient, a physicochemical property connected to the rates of biodegradation processes of polycyclic aromatic hydrocarbons.