The estimation of electron affinities fromab initio 1s orbital energies

Summary It has been found that the electron affinities of alkoxy-radicals can be estimated using a correlation with the 1s orbital energy of the oxygen on the associated alkoxy-anion, EA=–0.64503 * (1s orbital energy) –351.58. The method assumes that the species of interest accepts the electron into an orbital which is localized on the oxygen.     

Atomic ionization potentials and electron affinities with relativistic and mass corrections

Relativistic corrections to ionization potentials (IPs) and electron affinities (EAs) of atoms with an atomic number Z≤54 are examined based on the first-order perturbation theory with an approximate Schr?dinger form of the Dirac-Coulomb-Breit Hamiltonian. Using a Hartree-Fock (HF) wave function from the numerical HF method as the unperturbed function, both the LS-non-splitting and fine-structure corrections are evaluated together with the normal and specific mass corrections. The LS-non-splitting corrections are found to be important for IPs and EAs of transition metal atoms. The fine-structure corrections are generally larger in magnitude than the LS-non-splitting corrections for the atoms of groups 13–18 with Z≥31, and can never be neglected. Comparison of the IPs and EAs presented here and experimental IPs and EAs gives an estimation of the electron correlation correction for these properties. For some light atoms, the estimated values agree with the results directly obtained from correlated calculations. Received: 28 January 1997 / Accepted: 4 March 1997     

On the theoretical determination of the electron affinity of ozone

Summary Multiconfigurational electron correlation methods have been analyzed in order to theoretically compute the electron affinity (EA) of ozone. The near-degeneracy correlation effects, which are so important in O₃ and O ₃ ^– , have been described using complete active space (CAS) SCF wave functions. Remaining dynamic correlation effects are computed using second-order perturbation theory (the CASPT2 method). The best calculated adiabatic value (including zero-point energy corrections), 2.19 eV, is about 0.09 eV larger than the experimental value. Comparative studies using size-consistent coupled pair functional approaches (CPF and ACPF) have also been performed. The harmonic frequencies in O ₃ ^– have been determined to be: ₁=992, ₂=572, and ₃=879 cm^–1, which gives a zero-point energy of 0.151 eV.     

Electron affinities, excitation energies and ionization potentials of the transition metals (I) Sc and Ti

The electron affinities of the Sc and Ti atoms have been obtained by configuration interaction calculations. Energy convergence with respect to the systematic expansion of both the one-electron basis set and the configuration space was investigated for valence electrons, and the inclusion of correlation contributions from core electrons and relativistic effects gave the electron affinities of 0.181 eV and 0.163 eV for Sc and Ti, respectively. These are in excellent agreement with the observed values of 0.189 ± 0.020 eV and 0.080 eV. The same approach was applied for the first excited states and positive ions of both atoms. Excellent agreement with the experimental results was also obtained for these states. Received: 16 February 1998 / Accepted: 2 April 1998 / Published online: 23 June 1998     

Excitation energies, electron affinities and ionization potentials of the transition metals V, Cr and Mn

 Configuration interaction calculations were carried out for neutral ground and excited states and positively and negatively ionized states of the V, Cr and Mn atoms. Energy convergence with respect to systematic expansion of both the one-electron and configuration bases was investigated for valence correlation. Contributions from core electrons to the differential correlation energies and relativistic effects were evaluated separately. Assuming additivity of these contributions, excitation energies, electron affinities and ionization potentials of the atoms were obtained. All calculated values were in excellent agreement with the observed values within a deviation of 0.056 eV except for the electron affinity of the V atom, which had a calculated value 0.110 eV larger than the experimental value. Received: 9 August 2000 / Accepted: 26 October 2000 / Published online: 3 April 2001     

Structures, vibrational frequencies, and electron affinities of SF5On/SF5On (n = 1–3)

The molecular structures, vibrational frequencies, and electron affinities of the SF₅O_n/SF₅O_n⁻ (n = 1–3) species have been examined with four hybrid density functional theory (DFT) methods. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. The SF₅O_n (n = 1–3) species should be potential greenhouse gases. The anion SF₅O₂⁻ with C_s symmetry has a ³A″ electronic state, and the neutral SF₅O₃ with ²A″ electronic state has C_s symmetry. The anions SF₅O₂⁻ and SF₅O₃⁻ should be regarded as SF₅⁻·O₂ and SF₅O⁻·O₂ complexes, respectively. Three different types of the neutral–anion energy separation presented in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The EA_ad values predicted by the B3PW91 method are 5.22 (SF₅O), 4.38 (SF₅O₂), and 3.61 eV (SF₅O₃). Compared with the experimental vibrational frequencies, the BHLYP method overestimates the frequencies, and the other three methods underestimate the frequencies. The bond dissociation energies D_e (SF₅O_n → SF₅O_n−m + O_m) for the neutrals SF₅O_n and D_e (SF₅O_n⁻ → SF₅O_n−m⁻ + O_m and SF₅O_n⁻ → SF₅O_n−m + O_m⁻) for the anions SF₅O_n⁻ are reported.     

Theory and computation of electron transfer reorganization energies with continuum and molecular solvent models

Contemporary continuum-based models of solvation in polar media are surveyed and assessed, with special focus on non-equilibrium solvation. A new hybrid approach combining molecular-level treatment of inertial solvent response, and inclusion of inertialess solvent response at the continuum level, is presented and illustrated in terms of calculated equilibrium solvation free energies for small molecular ions and reorganization free energies for model dumbbell systems.     

Structures, electron affinities, and vibrational frequencies of the mono-, di-substituted SF6 radicals

Optimized molecular structures, electron affinities, and IR-active vibrational frequencies have been predicted using five different hybrid Hartree–Fock/density functional theory (DFT) methods for a series of mono-, di-substituted SF₆ compounds. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated [J.C. Rienstra-Kiracofe, G.S. Tschumper, H.F. Schaefer, S. Nandi, G.B. Ellison, Chem. Rev. 102 (2002) 231]. The equilibrium configurations of the anions and are found to be a zigzag geometry with ²A electronic state. Three different types of the neutral-anion energy separation reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities of the mono-, di-substituted SF₆ compounds obtained at the KMLYP function are 1.48 eV (SF₆), 3.20 eV (SF₅Cl), 3.49 eV (SF₅Br), 1.59 eV (SF₅CF₃), 3.21 eV (CF₃SF₄Cl), 3.59 eV (CF₃SF₄Br), 1.36 eV (CF₃SF₄CH₃), 2.32 eV (CF₃SF₄CF₃), respectively.     

On the evaluation of molecular electron affinities by approximate density functional theory

The ability of approximate Density Functional Theory to calculate molecular electron affinities has been probed by a series of calculations on the hydrides CH₃, NH₂, OH, and HC₂ as well as the multibonded species CN, BO, N₃, OCN, and NO₂. The simple Hartree–Fock Slater scheme lacks dynamic correlations and underestimates on the average the adiabatic electron affinities (EA_ad) by 0.7 eV. A considerable improvement is obtained by the Local Density Approximation (LDA) in which dynamic correlation is included. Values from LDA calculation underestimate, on the average, the adiabatic electron affinities by 0.4 eV. The best agreement with experiment is obtained by the LDA/NL scheme in which a nonlocal correction recently proposed by Becke is added to the LDA energy expression. The LDA/NL method underestimates EA_ad by 0.2 eV. It is concluded that the LDA/NL method affords EA_ad's in as good agreement with experiment as ab initio techniques in which electron correlation is taken into account by extensive configuration interaction. A full geometry optimization has been carried out on the nine neutral sample molecules as well as the corresponding anions.     

DFT study on the electron affinities of the chlorinated benzenes

The molecular structures and electron affinities of the C₆HCl₅ and C₆Cl₆ molecules have been determined using seven pure Density Functional Theory (DFT) or hybrid Hartree–Fock/DFT methods. The EAs of ten kinds of monochlorobenzene, dichlorobenzene, trichlorobenzene and tetrachlorobenzene are also predicted. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem. Rev. 2002, 102, 231). The geometries are fully optimized with each DFT method independently. The equilibrium configuration of hexachlorobenzene is found to be planar with D_6h symmetry. The pentachlorobenzene is planar with C_2υ symmetry. Three different types of the neutral-anion energy separations reported in this work are the adiabatic Electron Affinity (EA_ad), the vertical Electron Affinity (EA_vert), and the Vertical Detachment Energy (VDE). The most reliable adiabatic electron affinities of the chlorinated benzenes obtained at the BHLYP level of theory are −0.18 eV (C₆H₅Cl), 0.07 eV (1,2-C₆H₄Cl₂), 0.07 eV (1,3-C₆H₄Cl₂), 0.04 eV (1,4-C₆H₄Cl₂), 0.29 eV (1,2,3-C₆H₃Cl₃), 0.31 eV (1,2, 4-C₆H₃Cl₃), 0.31 eV (1,3,5-C₆H₃Cl₃), 0.51 eV (1,2,3,4-C₆H₂Cl₄), 0.48 eV (1,2,4,5-C₆H₂Cl₄), 0.50 eV (1,2,3,5-C₆H₂Cl₄), 0.74 eV (C₆HCl₅) and 0.79 eV (C₆Cl₆), respectively.     

Preparation of ferrocenes with high fluorous-phase affinities

The reaction of 1,1′-bis(pentafluorophenyl)ferrocene with fluorous alkoxides having the general formula NaOCH₂(CF₂)_nCF₃ (n = 0, 2, 5, 7, and 8) afforded a series of ferrocenes of general formula {η⁵-4-[CF₃(CF₂)_nCH₂O]C₆F₄C₅H₄}₂Fe (1). The reaction of 1,1′-bis(4-tetrafluoropyridyl)ferrocene with the same fluorous alkoxides afforded a series of ferrocenes of general formula (η⁵-4-{2,6-[CF₃(CF₂)_nCH₂O]₂C₅F₂N}C₅H₄)₂Fe (2). Perfluoro(methylcyclohexane)/toluene partition coefficients increase with the number (2 or 4) and length (n) of the fluorous substituent. Complexes 1a and 2a (both n = 0) were structurally characterized.     

On the computation and contribution of conductivity in molecular ionic liquids

In this study we present the results of the molecular dynamics simulation of the ionic liquids: 1-butyl-3-methyl-imidazolium tetrafluoroborate and trifluoromethylacetate as well as 1-ethyl-3-methyl-imidazolium dicyanamide. Ionic liquids are characterized by both a molecular dipole moment and a net charge. Thus, in contrast to a solution of simple ions in a (non-) polar solvent, rotational and translational effects influence the very same molecule. This study works out the theoretical framework necessary to compute the conductivity spectrum and its low frequency limit of ionic liquids. Merging these computed conductivity spectra with previous simulation results on the dielectric spectra of ionic liquids yields the spectrum of the generalized dielectric constant, which may be compared to experiments. This spectrum was calculated for the three ionic liquids over six orders of magnitude in frequency ranging from 10 MHz to 50 THz. The role of rotation and translation and their coupling term on the generalized dielectric constant is discussed in detail with a special emphasis on the zero-frequency limit. Thereby, the frequency dependence of the cross correlation between the collective rotational dipole moment and the current is discussed.     

DFT calculations of the ionization potentials and electron affinities of serinamide

Adiabatic and vertical ionization potentials (IPs) and valence electron affinities (EAs) of serinamide in the gas phase have been determined using density functional theory (DFT) B3LYP, B3P86, and B3PW91 methods with the 6‐311++G** and 6‐311G** basis sets, respectively. IPs and EAs of serinamide in solution have been calculated with the B3LYP method using the 6‐311++G** and 6‐311G** basis sets. Eight possible conformers of serinamide and its charged states in the gas phase have been optimized employing the DFT B3LYP method with 6‐311++G** and 6‐311G** basis sets, respectively. All the adiabatic and vertical ionization potentials (AIPs and VIPs) of eight serinamide conformers in our work are positive values, whether in the gas phase or in solutions; the IPs in solutions are smaller than the results in the gas phase and decrease with increased dielectric constants in solutions. This finding indicates that the cationic states in solutions are more stable than those in the gas phase. All EAs of eight serinamide conformers are negative values in the gas phase, indicating that the anionic states are unstable with respect to electron autodetachment, both adiabatically and vertically. In contrast, all other adiabatic electron affinities (AEAs) are negative values in solutions except for 6S in water; 7S in chloroform, acetone, and water; and 8S in acetone and water, and increase with increasing of dielectric constants in solutions. All vertical electron affinities (VEAs) are negative values in solutions; however, no good rule has been found for these values in solutions. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

On the nonexistence of strictly diabatic molecular electronic bases

In a recent publication (M. Baer, A. Alijah, Chem. Phys. Lett. 319 (2000) 489), it is proposed that, contrary to a number of statements in the literature, it may indeed be possible to construct strictly diabatic electronic basis sets in molecular systems. We show that the result of Baer and Alijah is invalid.     

The evaluation of molecular electron affinities

The performance of a variety of levels of theory in evaluating molecular electron affinities (EAs) has been systematically examined. Calculations have been carried out for six different basis sets and for nine theoretical procedures including unrestricted (UHF) and restricted (RHF) Hartree-Fock theory, Møler-Plesset perturbation theory (UMP2, UMP3, UMP4), configuration interaction (UCISD, RCISD, RCISD(Q)) and equations-of-motion (EOM) approaches. Electron affinities were evaluated for CH₃, NH₂, OH, F, C₂H, CN, BO, N₃, OCN, and NO₂. Very poor results are generally obtained unless diffuse functions are included in the basis set and electron correlation is incorporated. Even with the largest basis set used in the present study (6-311 + + G(2d, 2p)), there are still residual errors greater than 0.2 eV (UMP4) or 0.6 eV (CISD) in the absolute EAs. However, better results are obtained under certain circumstances for relative EAs. The results appear to be significantly affected by spin contamination in the UHF wave-functions. For those systems for which spin contamination is small, best absolute values of the EAs generally come from the EOM and UMP2 calculations, whereas the most constant errors (thereby allowing systematic correction) are found at the UMP4, CISD, and RCISD(Q) levels. For the systems for which spin contamination is larger, best results are obtained with the CI-based procedures (CISD and RCISD(Q)). The errors in calculated EAs for the molecules with differing electronic characteristics can vary quite widely. Caution must therefore be exercised before applying schemes which rely on a constancy of errors to estimate electron affinities. The UMP procedures appear particularly suspect in this regard if spin contamination is significant. The RCISD(Q) approach is recommended under such circumstances.     

Calculation of the enthalpies of formation and proton affinities of some isoquinoline derivatives

Ab initio molecular orbital theory has been used to calculate enthalpies of formation of isoquinoline, 1-hydroxyisoquinoline, 5-hydroxyisoquinoline, and 1,5-dihydroxyisoquinoline as well as some pyridine and quinoline derivatives. The proton affinities of the four isoquinoline derivatives were also obtained. The high-level composite methods G3(MP2), G3(MP2)//B3LYP, G3//B3LYP, and CBS-QB3 have been used for this study, and the results have been compared with available experimental values. For six of the eight studied compounds, the theoretical enthalpies of formation were very close to the experimental values (to within 4.3 kJ · mol⁻¹); where comparison was possible, the theoretical and experimental proton affinities were also in excellent agreement with one another. However, there is an extraordinary discrepancy between theory and experiment for the enthalpies of formation of 1-hydroxyisoquinoline and 1,5-dihydroxyisoquinoline, suggesting that the experimental values for these two compounds should perhaps be re-examined. We also show that popular low cost computational methods such as B3LYP and MP2 show very large deviations from the benchmark values.     

Protonation of glycine and alanine: proton affinities, intrinsic basicities and proton transfer path

Proton affinities and intrinsic basicities for nitrogen and oxygen protonation in the gas phase of the amino acids glycine and alanine were calculated using density functional theory (DFT) and ab initio methods at different levels of theory from Hartree-Fock (HF) to G2 approximations. All methods gave good agreement for proton affinities for nitrogen protonation for both amino acids. However, dramatic differences were found between DFT, MP4//MP2, and G2 results on one hand, and MP4//HF results on the other to the calculation of structural and energetic characteristics of oxygen protonation in glycine and alanine. An investigation into the source of these differences revealed that electron correlation effects are chiefly responsible for the differences in calculated oxygen proton affinities between the various methods. It has been found that proton transfer between nitrogen and oxygen protonation sites in both amino acids occurs without a transfer path barrier when correlated methods were used to calculate the path energetics.     

Determination of NO chemical affinities of benzyl nitrite in acetonitrile

There is an increasing interest in the study of NO chemical affinities of organic nitrites, for the biological and physiological effects of organic nitrites seem to be due to their ability to release NO. In this paper, NO chemical affinities of ten substituted benzyl nitrites were determined by titration calorimetry combined with a thermodynamic cycle in acetonitrile solution. The results show that ΔH _het(O-NO)s of benzyl nitrites are substantially larger than the corresponding ΔH _homo(O-NO)s, suggesting that these O-nitroso compounds much more easily release NO radicals by the O-NO bond homolytic cleavage. It is believed that the structural and energetic information disclosed in this work should be useful in understanding chemical and biological functions of organic nitrites. __________ Translated from Chemical Journal of Chinese Universities, 2007, 28(12): 2327–2329