Electron Affinities Of Atoms Research Articles

Accurate calculation of the electron affinities of the group-13 atoms

Using a form of multireference single and double configuration-interaction method as CIPSI, we have tested the ability to obtain accurate values of the electron affinity for non-first-row elements by computing the electron affinity of the group-13 atoms Al, Ga, In, and Tl using pseudopotentials to describe the core electrons, and an extended basis set for the valence electrons. Our results show that it is possible to obtain precise values of the electron affinities of these atoms using the CIPSI method (Al=0.45, Ga=0.29, In=0.38, and Tl=0.27 eV), and that the error induced by the use of pseudopotentials in the CIPSI electron afinities is very small.

Electron affinities of the first-row atoms revisited. Systematic basis sets and wave functions

The calculation of accurate electron affinities (EAs) of atomic or molecular species is one of the most challenging tasks in quantum chemistry. We describe a reliable procedure for calculating the electron affinity of an atom and present results for hydrogen, boron, carbon, oxygen, and fluorine (hydrogen is included for completeness). This procedure involves the use of the recently proposed correlation-consistent basis sets augmented with functions to describe the more diffuse character of the atomic anion coupled with a straightforward, uniform expansion of the reference space for multireference singles and doubles configuration-interaction (MRSD-CI) calculations. Comparison with previous results and with corresponding full CI calculations are given. The most accurate EAs obtained from the MRSD-CI calculations are (with experimental values in parentheses) hydrogen 0.740 eV (0.754), boron 0.258 (0.277), carbon 1.245 (1.263), oxygen 1.384 (1.461), and fluorine 3.337 (3.401). The EAs obtained from the MR-SDCI calculations differ by less than 0.03 eV from those predicted by the full CI calculations.

Hydrogen-induced surface acceptors on GaAs(100) surfaces at low temperatures

The interaction of atomic hydrogen with clean, cleaved GaAs(110) surfaces was investigated at temperatures of 140 ± 10 K. Ultraviolet photoemission spectroscopy, a Kelvin probe and electric-field-induced Raman spectroscopy were used to determine both the changes of surface band-bending and of the ionization energy as a function of exposure to atomic hydrogen. Up to the largest hydrogen exposure equivalent to 10 5 L of molecular hydrogen the ionization energy is decreased by 1.1 ± 0.05 eV on samples doped n- and p-type. On n-samples the Fermi level eventually becomes pinned at 0.54 ± 0.07 eV above the top of the valence band for exposures larger than 10 2 L. A depletion layer exhibiting a surface band-bending of 0.2 ± 0.07 eV initially forms on samples doped p-type but was found to vanish gradually for exposures larger than 10 L. Thus atomic hydrogen generates surface states of acceptor character on GaAs(110) surfaces at low temperatures. The energy level of the hydrogen-induced surface acceptors is in reasonable agreement with theoretical predictions and it confirms a correlation between the energy levels of the adsorbate-induced surface acceptors and the atomic electron affinities of the adatoms. These results clearly show that with hydrogen no electronic passivation of GaAs interfaces can be achieved.

Calculation of the second electron affinities of atoms

The second electron affinities of the atoms helium to krypton are calculated using the self-interaction corrected generalized exchange local-spin-density functional theory with the correlation energy functional. The dependence of the second electron affinities of the elements O, S, and Se on the Watson sphere radius is discussed. The present results are compared with other theoretical values and experimental data for the elements helium through krypton. Keywords: second electron affinity, density functional theory.

Fermi and Coulomb correlated relativistic local-density method for atoms

A parameter-free local-density method called the \ensuremath{\Xi} method was developed earlier for atoms [N. Vaidehi and M. S. Gopinathan, Phys. Rev. A 29, 1679 (1984)]. This method, which considered only the Fermi correlation in the potential, was shown to be close to Hartree-Fock accuracy. Its relativistic extension [V. Selvaraj and M. S. Gopinathan, Phys. Rev. A 29, 3007 (1984)] was also shown to give results that were close to Dirac-Hartree-Fock accuracy. In the present article, the relativistic \ensuremath{\Xi} method is modified by incorporating the spin-orbit interaction term in the Hamiltonian and the Coulomb correlation between the electrons of opposite spin. Using this fully correlated relativistic method, total energy, expectation values of ${r}^{n}$ (n=-1,1,2), and spin-orbit parameters for various atoms are calculated. Correlation energies for all the atoms in the Periodic Table are reported. Ionization energy and electron affinity of atoms are also discussed.

Theoretical study of the structures and electron affinities of the dimers and trimers of the group IB metals (Cu, Ag, and Au)

The molecular structure of both the neutral and negatively charged diatomic and triatomic systems containing the Cu, Ag, and Au metals are determined from ab initio calculations. For the neutral triatomic systems, the lowest energy structure is found to be triangular. The relative stability of the 2A1 and 2B2 structures can be predicted simply by knowing the constituent diatomic bond distances and atomic electron affinities (EAs). The lowest energy structure is linear for all of the negative ions. For anionic clusters containing Au, the Au atom(s) preferentially occupy the terminal position(s). The EAs of the heteronuclear systems can be predicted relatively accurately from a weighted average of the corresponding homonuclear systems. Although the theoretical EAs are systematically too small, accurate predictions for the EAs of the triatomics are obtained by uniformly scaling the ab initio results using the accurate experimental EA values available for the atoms and homonuclear diatomics.

Electron affinities of alkaline-earth atoms by means of different density functionals.

Various correlation energy density functionals have been used to evaluate the electron affinities of the alkaline-earth atoms. A related approach based on polarization potentials was also tested. The results give evidence for the existence of stable negative ions of the atoms Ca, Sr, and Ba. The various density functionals perform relatively well yielding qualitatively correct predictions.

Effect of the correlation correction on the ionization potential and electron affinity in atoms.

The generalized-exchange local-spin-density-functional theory (LSD-GX) with self-interaction correction has been used to calculate the ionization potentials for the atoms (atomic number Z from 2 to 38) and the electron affinities for some selected atoms. The effects of the Coulomb correlation correction and relaxation on the ionization potential and electron affinity are discussed using the Stoll, Pavlidou, and Preuss [Theor. Chim. Acta 49, 143 (1978)] correlation-energy expression, and the Vosko, Wilk, and Nusair (VWN) [Can. J. Phys. 58, 1200 (1980)] expression. The theoretical results are compared to experiment. The LSD-GX theory with VWN correlation correction is the best method for calculating ionization potentials and electron affinities for atoms.

Electronic properties of sulfur adsorbed on cleaved GaAs surfaces

The interaction of molecular S2 with cleaved GaAs(110) surfaces was followed by using a Kelvin probe and ultraviolet photoemission spectroscopy. The adsorption of sulfur increases the ionization energy of the cleaved surfaces by up to 0.92 eV and causes a Fermi-level pinning at 0.34 eV above the valence-band top for both types of doping. The sign of the change of the ionization energy can be explained by a chemical charge transfer between the adsorbed sulfur and adsorbate-induced gap states, since sulfur is more electronegative than GaAs. The sulfur-related pinning position of the Fermi level is located below the charge-neutrality level of the virtual gap states (ViGS) of the complex GaAs band structure, where the ViGS predominantly possess donor character. This result confirms the predictions from the ViGS model of adsorbate-induced gap states. The energy of the sulfur as well as the oxygen- and chlorine-related surface states, which are of the acceptor type, correlate with the respective atomic electron affinities.

Variational Quantum Monte Carlo Calculation of Materials Properties

AbstractA new method of calculating the total energy and other ground-state properties of solids which employs nonlocal pseudopotentials in conjunction with the variational quantum Monte Carlo approach is presented. Valence electron correlations are treated using the exact interaction with a correlated many-electron wavefunction of the Jastrow-Slater form. The use of pseudopotentials for the electron-ion interaction removes from the problem the large fluctuations of electron energies in the core region which occur in quantum Monte Carlo all-electron schemes. We discuss calculation of the cohesive energy and structural properties of diamond and graphite and the ionization energy and electron affinity of atoms using the present approach. The results are in excellent agreement with experiment.

Staebler-wronski effect: A solution

A scanning of various elements of the periodic table has been made keeping in view their atomic sizes, electron affinities and ionization energies. The halogens belonging to group vii have been suggested as the most effective elements to be incorporated in a-Si:H films to contain photoinduced degradation problems in them.

A non local density functional calculation of the diamagnetic susceptibilities and other electronic properties of noble gases and closed-shell ions

The non local weighted-density approximation (WDA) to the exchange-correlation potentialVxc(r) is used to compute electron densities, ionization potentials and electron affinities of several atoms and ions. Especial care is taken in calculating and discussing 〈r2〉 in noble gas atoms. Good results are obtained for all those quantities, but it is critical that the WDA is applied in such a way that it preserves the correct larger behaviour ofVxc(r). A comparison of the calculated electron density with that of the Hartree-Fock method shows the effects of coulomb correlation. The density rearrangements upon the introduction of correlation agree qualitatively with the results of Configuration-Interaction calculations

ChemInform Abstract: Predicted Stabilities of Monatomic Anions in Water and Liquid Ammonia at 298.15 K

Abstract Critically evaluated experimental and theoretical atomic electron affinities are assembled and used to derive thermodynamic properties of gas-phase monatomic anions throughout the Periodic Table. The stabilities (as ΔGof) of these anions in water and liquid ammonia are calculated by a semiempirical electrostatic model. The predictions are compared with experimental observations where possible.

A note on the accuracy of correlation energy estimation by local approximation: first ionization energies and electron affinities of light atoms

A local spin density functional estimate of the pure correlation energy is added to Hartree-Fock values for the ionization energy and electron affinity of the first eighteen atoms. The local correlation estimate is found to yield a useful improvement in accuracy which augurs well for the application of the same method to molecules.

An application of correlation energy density functionals to atoms and molecules

Four density functionals — including that recently introduced by Perdew ((1986) Phys Rev B33: 8822)—are tested for first-row atoms, hydrides and dimers. Calculated contributions of the correlation energy to the ionization potentials and electron affinities of atoms and to the dissociation energies of molecules are compared with “empirical” values which were reevaluated for this purpose. An improvement over Hartree-Fock is found in all cases if the self-interaction or the gradient correction are included in the density functional, although there is a rather large variation in the accuracy of the predictions.

Nonlocal density functional calculation of the electron affinity of atoms

The weighted-density approximation (WDA) to the exchange-correlation potential V xc ( r ) is used to compute electron affinities of atoms within the context of density functional theory. Good results are obtained for the affinities of H, O and F, but it is critical that the WDA must be applied in such a way as to preserve the correct asymptotic behaviour of V xc ( r ).

The ionization potentials of F2: A comparison of multiconfigurational electron propagator (MCEP) with other large scale methods using the same basis set

The multiconfigurational electron propagator technique (MCEP) gives reliable vertical ionization potentials (I.P.s) and electron affinities (E.A.s) for atoms and molecules, including open-shell and highly correlated systems. Shake-up and inner-valence I.P.s can be accurately obtained and characterized. In contrast, perturbative-type Green’s function (PTGF) approaches are useful for closed-shell systems with relatively little correlation. Perturbative-type Green’s functions cannot consistently reliably predict shake-up and inner-valence I.P.s. We have applied the MCEP method to F2 at 2.68 a.u. using 〈4s3p1d〉 and 〈5s4p2d〉 basis sets. In F2, the complete active space of all valence orbitals is small. Hence, reliable MCEP results should be obtained for all valence ionization processes. In addition, comparison calculations are given using other large scale techniques, i.e., ΔSCF, ΔMCSCF, PTGF, and Δ multireference CI using the same basis sets. The photoelectron spectrum of F2 below 30 eV is not well characterized experimentally except for the three lowest principal peaks, and apparently no reliable spectra have been reported for higher energies. We report and characterize several I.P.s in F2 0–60 eV, including several I.P.s that have not as yet been observed experimentally.

Predicted stabilities of monatomic anions in water and liquid ammonia at 298.15 K

Critically evaluated experimental and theoretical atomic electron affinities are assembled and used to derive thermodynamic properties of gas-phase monatomic anions throughout the Periodic Table. The stabilities (as ΔGof) of these anions in water and liquid ammonia are calculated by a semiempirical electrostatic model. The predictions are compared with experimental observations where possible.

Binding Energies in Atomic Negative Ions: II

This article updates a ten-year-old review of this subject [J. Chem. Phys. Ref. Data 4, 539 (1975)]. A survey of the electron affinity determinations for the elements up to Z=85 is presented, and based upon these data, a set of recommended electron affinities is established. Recent calculations of atomic electron affinities and the major semiempirical methods are discussed and compared with experiment. The experimental methods which yield electron binding energy data are described and intercompared. Fine structure splittings of these ions and excited state term energies are given.

Basis set and electron correlation effects on the electron affinities of first row atoms

The electron affinities of boron, carbon, oxygen, and fluorine atoms have been evaluated by Mo/ller–Plesset perturbation calculations through complete fourth order using several large basis sets. The convergence of the perturbation series has been evaluated carefully by means of modified coupled cluster methods. Large basis sets and electron correlation effects involving higher substitutions are found to be important in the accurate calculation of electron affinities. Triple substitutions are particularly important in the correlation treatment, contributing more than 0.2 eV to the electron affinities of O and F. The electron affinities of all the systems are calculated to be within 0.1 eV of the corresponding experimental values.