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     

DFT study of ionization potentials and electron affinities of formamide and its methylation derivatives

The ionization potentials (IPs) and electron affinities (EAs) of formamide in the gas phase have been calculated using density functional theory (DFT), ab initio HF and Møller-Plesset perturbational theory (MP) at 6-311++G** basis set. The results indicate that the IPs of formamide obtained with DFT and MP are in agreement with the results obtained from experiment. And B3LYP has been confirmed to be the most accurate method in calculating the AIPs and VIPs of formamide through our work. IPs and EAs of formamide in solution are not known experimentally, therefore IPs and EAs of formamide in chloroform, acetone, and dimethylsulfoxide have been calculated using polarized continuum model (PCM) with B3LYP/6-311++G** level and have been compared with the values in the gas phase. The AIPs and VIPs of formamide have been compared with those of its methylation derivatives. All EAs of methylation derivatives of formamide are bigger than those of formamide conformers in the gas phase with BLYP, B3LYP, and B3P86 methods at 6-311++G** basis set. All these indicate that all anions of methylation derivatives of formamide are more stable than anions of formamide with respect to electron detachment adiabatically and vertically in the gas phase.     

A semi-empirical MO theory for ionization potentials and electron affinities

A method for calculating the vertical ionization potentials and electron affinities according to their fundamental definition as differences between energies of the singlet ground and doublet ionized states is developed for cyclic hydrocarbons. The method adopts a new approach based on the central idea of a recent ab initio IP and EA calculation in which orbital exponents are optimized for both ground and ionized states. Hence, all the semi-empirical parameters of the MO theory are written as functions of the effective nuclear charge which, in turn, is made self-consistent with the molecular electronic charge distribution of the species. Although the MO theory is developed in the π electron approximation, the changes in the σ electron density, resulting from the loss or gain of a π electron, are explicitly considered in the calculation. The theory is compared to the earlier work of Hoyland and Goodman and tested against the first five polyacenes and on the condensed ring aromatics phenanthrene, pyrene, and perylene. Except for perylene, the results are in close agreement with the latest photoelectron spectroscopic measurements.     

Theoretical study of electron affinities,ionization potentials and photoionization cross-sections of chalcogen heterocyclopentadienes

The first electron affinities, valence ionization potentials and photoionization cross-sections of furan, thiophene, selenophene and tellurophene have been studied by application of one-particle Green's function technique and plane-wave theory, respectively, within the framework of the CNDO approximation. The results are compared with the available experimental values and some sophisticated ab initio predictions.     

Analysis of the equation-of-motion theory of electron affinities and ionization potentials

An analysis of the equation-of-motion (EOM) method for computing molecular electron affinities and ionization potentials is presented. The method is compared with the Dyson equation approach of Green function theory. Particular emphasis is devoted to clarifying the similarities between these two theories when carried out to second and to third order. The Epstein—Nesbet hamiltonian and the notion of diagonal scattering renormalization have been used to systematize this comparison.     

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     

The density functional theory study on the ionization potentials and electron affinities of cytosine-formamide complexes

Accurate adiabatic and vertical ionization potentials (IPs) and valence electron affinity (EA) of cytosine and cytosine-formamide complexes have been determined using density functional theory B3LYP. Comparison has been made with the data from a recently published study, as well as earlier studies on cytosine. For cytosine-formamide complexes it is found that the hydrogen bond interactions between cytosine and formamide play a more important role in the process of electron attachment than in the process of electron detachment. Meanwhile, the hydrogen bond interactions facilitate the adiabatic electron detachment and attachment but have different effects on the vertical electron detachment and attachment with different positions of formamide. The article is published in the original.     

Theoretical study on isomeric stabilities of C2H2Si and its ionization potentials and electron affinities

The geometric structures and isomeric stabilities of various stationary points in C(2)H(2)Si neutral and its cation and anion are investigated at the coupled-cluster singles, doubles (triples) [CCSD(T)] level of theory. For the geometrical survey, the basis sets used are of the Dunning's correlation consistent basis sets of triple-zeta quality (cc-pVTZ) for the neutral and cation. For the anions, the cc-pVTZ basis sets with diffuse functions (aug-cc-pVTZ) are used. The final energies are calculated by the use of the CCSD(T) level of theory with the aug-cc-pVTZ basis set at their optimized geometries. To lower lying neutrals and cations, the Dunning's correlation consistent basis sets of quadruple-zeta quality (cc-pVQZ) are also applied. Both the global minima of the C(2)H(2)Si neutral and cation, N-1 (C(2v):(1)A(1)) and C-1 (C(2v):(2)B(2)), respectively, are silacyclopropenylidene conformers, having a CCSi ring with a C[Double Bond]C double bond. No competitive stable isomers exist in the present C(2)H(2)Si neutral. In the cation, however, the second lowest lying isomer C-2 lies 10.8 kJ/mol above the most stable C-1. The vertical and adiabatic ionization potentials from the lowest lying neutral N-1 are 9.83 and 8.97 eV, respectively, at the CCSD(T)/cc-pVQZ level of theory. The electron addition to the N-1 does not result in the anion with positive (real) electron affinities. On the other hand, the electron addition to the N-2 isomer produces the global minimum anion A-1 (C(2v):(2)B(1)) with the positive electron affinities of 1.13 eV. The second lowest lying anion isomer A-2 with silylenylacetylene conformer, produced from an electron addition to the N-3 neutral, very well competes with the A-1 after the zero-point vibrational energy corrections. The energy difference between the two lowest lying isomers of the neutral and its anion, N-1 and A-1, is only 0.39 eV.     

Coupling matrix element of electron self-exchange reactions in solution

On the basis of the common feature among the electron transfer process and the ion hydration process as well as the relevant experimental kinetic data of electron transfer reaction,a new accurate hydration potential function scheme for the determination of electron transfer coupling matrix element is presented.The coupling matrix element between two hydrated ions of the reacting system in solution is calculated.The results and the applicability of this scheme are discussed.     

Application of many-body rayleigh-schrödinger perturbation theory to calculation of ionization potentials and electron affinities

The ionization potentials and electron affinities are calculated by the use of the many-body Rayleigh-Schrödinger perturbation theory. This approach is elaborated up to the third order, where each perturbation contribution can be interpreted by the diagrammatic method. Some simple illustrative calculations of π-electron systems are carried out.     

Localized orbital corrections for the calculation of ionization potentials and electron affinities in density functional theory

This paper describes the extension of a previously reported empirical localized orbital correction model to the correction of ionization potential energies (IP) and electron affinities (EA) for atoms and molecules of first and second row elements. The B3LYP localized orbital correction version of the model (B3LYP-LOC) uses 22 heuristically determined parameters that improve B3LYP DFT IP and EA energy calculations on the G2 data set of 134 molecules from a mean absolute deviation (MAD) from experiment of 0.137 to 0.039 eV. The method significantly reduces the number of outliers and overall MAD to error levels below that achieved with G2 wave function based theory; furthermore, the new model has zero additional computational cost beyond standard DFT calculations. Although the model is heuristic and is based on a multiple linear regression to experimental errors, each of the parameters is justified on physical grounds, and each provides insight into the fundamental limitations of DFT, most importantly the failure of current DFT methods to accurately account for nondynamical electron correlation.     

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     

Overlapping spheres multiple scattering Xα calculations of the ionization potentials and electron affinities of nitrogen oxides

The ionization potentials and electron affinities of a series of nitrogen oxygen compounds have been calculated by the overlapping spheres MS Xα method to assess its applicability on a series for which good experimental data is available. The results for the ionization potentials were satisfactory although a straightforward matching of calculated and experimental IP's without consideration of other criterion would have led to some misassignments. The results for the electron affinities are in excellent agreement with experiment.     

Carbazole and trinitrofluorenone: an ab initio investigation of ionization potentials,electron affinities and excited states

Minimal basis set SCF calculations are reported for the ground states and positive and negative ions of carbazole and tirnitrofluorenone. For carbazole, wavefunctions for several low-lyng excited states have also been obtained. Methods for surmounting convergence difficulties for these large systems are discussed. Relaxation effects in the calculations of excitations energies are considered and found to be significant. Calculated energies are compared to experimental results.     

Application of multiconfigurational many-body perturbation theory to the calculation of ionization potentials,electron affinities and excitation energ

Multiconfigurational many-body perturbation theory is applied to the problem of calculating ionization potentials, electron affinities, and excitation energies. H₂O, C₂H₄, and H₂ are studied, with correlation corrections through third order and inclusive of certain higher-order terms. Results are compared with those by other many-body theoretical methods.     

The self-consistent determination of the ion and neutral molecule wavefunctions in a theory of electron affinities and ionization potentials

In this paper, we discuss the validity of our earlier derivation of a theory of molecular electron affinities and ionization potentials. We show how one can improve upon our original derivation, which was not entirely consistent, by iteratively calculating both the ion and neutral molecule wavefunctions. Most importantly, we demonstrate that the electron affinities and ionization potentials which are obtained by using our original theory are correct through third order, even though the derivation of this theory contains an inconsistency.