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1.
A comprehensive study of single and double core ionization potentials of the aminophenol molecule is reported. The role of relaxation, correlation, relativistic, and basis set effects in these potentials is clarified. Special attention is paid to the isomer dependence of the single and double core ionization potentials. Some of them are also compared with the respective values of the phenol and aniline molecules. It is shown that the core level single ionization potentials of the para-, meta-, and ortho-aminophenol molecules differ only slightly from each other, rendering these structural isomers challenging to distinguish for conventional x-ray photoelectron spectroscopy. In contrast, the energy needed to remove two core electrons from different atoms depends noticeably on the mutual arrangement and even on the relative orientations of the hydroxyl and amine groups. Together with the electrostatic repulsion between the two core holes, relaxation effects accompanying double core ionization play a crucial role here. The pronounced sensitivity of the double ionization potentials, therefore, enables a spectroscopic characterization of the electronic structure of aminophenol isomers by means of x-ray two-photon photoelectron spectroscopy. 相似文献
2.
An attempt to construct a multiple core‐hole state within the optimized effective potential (OEP) methodology is presented. In contrast to the conventional Δ‐self‐consistent field method for hole states, the effects of removing an electron is achieved using some orthogonality constraints imposed on the orbitals so that a Slater determinant describing a hole state is constrained to be orthogonal to that of a neutral system. It is shown that single, double, and multiple core‐hole states can be treated within a unified framework and can be easily implemented for atoms and molecules. For this purpose, a constrained OEP method proposed earlier for excited states (Glushkov and Levy, J. Chem. Phys. 2007, 126, 174106) is further developed to calculate single and double core ionization energies using a local effective potential expressed as a direct mapping of the external potential. The corresponding equations, determining core‐hole orbitals from a one‐particle Schrödinger equation with a local potential as well as correlation corrections derived from the second‐order many‐body perturbation theory are given. One of the advantages of the present direct mapping formulation is that the effective potential, which plays the role of the Kohn–Sham potential, has the symmetry of the external potential. Single and double core ionization potentials computed with the presented scheme were found to be in agreement with data available from experiment and other calculations. We also discuss core‐hole state local potentials for the systems studied. © 2012 Wiley Periodicals, Inc. 相似文献
3.
Single-configuration relativistic Hartree–Fock values of the first ionization potentials for Cu through Kr7+, Ag through I6+, and Au through Pb3+ are computed in “frozen” and “relaxed core” approximations with and without allowance for core polarization. Effects of polarization of the atomic core by the valence electron are included by introducing a polarization potential in the one-electron Hamiltonian of the valence electron. The core polarization potential depends on two parameters, the static dipole polarizability of the core α and the cut-off radius r0, which are chosen independently of the ionization potential data. It is demonstrated that by including the core polarization potential with α and r0 parameters, which are simply chosen instead of being empirically fitted, it is still possible to account, on the average, for at least 70% of the discrepancy between the single-configuration relativistic Hartree–Fock ionization potentials and the experiment, a discrepancy usually ascribed to the contribution of valence-core electron correlations, and to bring the theoretical ionization potentials to an average agreement with experiment of around 1%. It can be concluded from this study that for low and medium Z elements the core polarization dominates for neutral systems or systems in low ionization stages, whereas for highly ionized systems the relativistic effects prevail. For heavy elements, however, the core polarization influence is comparable to the relativistic one only for neutral systems, whereas for ions the relativistic effects are overwhelmingly predominant. 相似文献
4.
An analytic scheme for the computation of scalar-relativistic corrections to nuclear forces is presented. Relativistic corrections are included via a perturbative treatment involving the mass-velocity and the one-electron and two-electron Darwin terms. Such a scheme requires mixed second derivatives of the nonrelativistic energy with respect to the relativistic perturbation and the nuclear coordinates and can be implemented using available second-derivative techniques. Our implementation for Hartree-Fock self-consistent field, second-order Moller-Plesset perturbation theory, as well as the coupled-cluster level is used to investigate the relativistic effects on the geometrical parameters and harmonic vibrational frequencies for a set of molecules containing light elements (HX, X=F, Cl, Br; H2X, X=O, S; HXY, X=O, S and Y=F, Cl, Br). The focus of our calculations is the basis-set dependence of the corresponding relativistic effects, additivity of electron correlation and relativistic effects, and the importance of core correlation on relativistic effects. 相似文献
5.
The orbital relaxation energy is defined for single and double ionizations of valence electrons, and is calculated for CH4, NH3, H2O and HF molecules with the ab initio SCF method. It is shown that the orbital relaxation energy for the ionization from a bonding orbital is about half of that for a non-bonding orbital, and the orbital relaxation energy for the double ionization is about double of that for the single ionization. This result gives a theoretical foundation for the empirical method of interpret Auger electron spectra by using experimental single ionization potentials. 相似文献
6.
K. B. Yatsimirskii 《Theoretical and Experimental Chemistry》1995,31(3):153-168
Relativistic effects become apparent when the velocity of the electron is arbitrarily close to the speed of light (137 au) without actually attaining it (in heavy atoms of elements at the end of Mendeleev's Periodic Table). At the orbital level, the relativistic effect is apparent in the radial contraction of penetrating s and p shells, expansion of nonpenetrating d and f shells, and the spin-orbit splitting of p-, d-, and f-shells. The appearance of a relativistic effect is indicated in the variation in the electronic configurations of the atoms in the Periodic Table, the appearance of new types of closed electron shells (6s1/2
2, 6p1/2
2, 7s1/2
2, 5d3/2
4), the stabilization of unstable oxidation states of heavy elements, the characteristic variation in the ionization enthalpies of heavy atoms, their electron affinity, hydration energies, redox potentials, and optical electronegativities. In the spectra of coordination compounds, a relativistic effect is observed when comparing the position of the charge transfer bands in analogous compounds, the parameters characterizing the ligand field strength (10Dq), the interatomic distances and angles in compounds of heavy elements. A relativistic effect is also apparent in the ability of heavy metals to form clusters and superclusters. Relativistic corrections also affect other properties of heavy metal compounds (force constants, dipole moments, biological activity, etc.).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 3, pp. 181–199, May–June, 1995. 相似文献
7.
The frozen local hole approximation (FLHA) is an adiabatic approximation which is aimed to simplify the correlation calculations of valence and conduction bands of solids and polymers or, more generally, of the ionization potentials and electron affinities of any large system. Within this approximation correlated local hole states (CLHSs) are explicitly generated by correlating local Hartree-Fock (HF) hole states, i.e., (N-1)-particle determinants in which the electron has been removed from a local occupied orbital. The hole orbital and its occupancy are kept frozen during these correlation calculations, implying a rather stringent configuration selection. Effective Hamilton matrix elements are then evaluated with the above CLHSs; diagonalization finally yields the desired correlation corrections for the cationic hole states. We compare and analyze the results of the FLHA with the results of a full multireference configuration interaction with single and double excitations calculation for two prototype model systems, (H2)n ladders and H-(Be)n-H chains. Excellent numerical agreement between the two approaches is found. Comparing the FLHA with a full correlation treatment in the framework of quasidegenerate variational perturbation theory reveals that the leading contributions in the two approaches are identical. In the same way it could be shown that a much less demanding self-consistent field (SCF) calculation around a frozen local hole fully recovers, up to first order, all the leading single excitation contributions. Thus, both the FLHA and the above SCF approximation are well justified and provide a very promising and efficient alternative to fully correlated wave-function-based treatments of the valence and conduction bands in extended systems. 相似文献
8.
Ph. Durand 《International journal of quantum chemistry》1986,29(4):915-935
Theoretical core effective potential methods are widely used in valence-only electron molecular calculations. These methods, which imply the frozen-core approximation, work well for the elements of the righthand side of the periodic table but are often unrealistic for metallic elements with highly polarizable cores. For these atoms one has to consider the polarization of the cores under the influence of the electric field created by the valence electrons. Moreover, relativistic corrections must be added for heavy atoms. Various theoretical approaches of core–valence interactions (polarization and core–valence correlations) will be reviewed, with a special emphasis on practical methods of calculation. The problem of handling the relativistic effects will mainly be discussed within the two-component Pauli formalism. It will be shown that the Foldy–Wouthuysen transformation is not the unique way for deriving relativistic corrections and that the second-order Dirac equation also provides a good starting point for obtaining relativistic corrections. Analytical exact results are given for the hydrogen atom. The accuracy of this approach is tested on many-electron atoms and molecules. It is finally shown that the problem of the core-valence separation is relevant to the general methodology of effective Hamiltonians that seems to provide the best promising way for filling the gap between the semiempirical and purely theoretical ab initio methods. 相似文献
9.
Nick Sablon Remigius Mastalerz Frank De Proft Paul Geerlings Markus Reiher 《Theoretical chemistry accounts》2010,127(3):195-202
The extent of relativistic effects on the Fukui function, which describes local reactivity trends within conceptual density functional theory (DFT), and frontier orbital densities has been analysed on the basis of three benchmark molecules containing the heavy elements: Au, Pb, and Bi. Various approximate relativistic approaches have been tested and compared with the four-component fully relativistic reference. Scalar relativistic effects, as described by the scalar zeroth-order regular approximation methodology and effective core potential calculations, already provide a large part of the relativistic corrections. Inclusion of spin–orbit coupling effects improves the results, especially for the heavy p-block compounds. We thus expect that future conceptual DFT-based reactivity studies on heavy-element molecules can rely on one of the approximate relativistic methodologies. 相似文献
10.
You Osanai Hirotake Ishikawa Nobuaki Miura Takeshi Noro 《Theoretical chemistry accounts》2001,105(6):437-445
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 相似文献
11.
In this work we calculate the photoelectron spectrum of the PtF(6)2- dianion by application of the third-order Dirac-Hartree-Fock one-particle propagator technique. Relativistic effects and electron correlation are hereby treated on a consistent theoretical basis which is mandatory for systems containing heavy elements. A PtF6(2-) gas phase photoelectron spectrum is not yet available and our calculations therefore have predictive character. As it is characteristic for dianionic systems a strong dependence on basis set size and molecular geometry is observed. In contrast to the already calculated PtCl(6)2- photoelectron spectrum no valence orbital inversion due to strong interplay of spin-orbit coupling and electron correlation is observed. Furthermore an unusually strong spin-orbit splitting was found for the sigma-type subvalence 1t1u molecular spinor despite its very small platinum p population. The double ionization threshold is strongly lowered by relativistic effects now enabling an interatomic Coulombic decay process after ionization from the sigma-bonding orbitals. The results stress the importance of spin-orbit coupling for the understanding of the spectral structure which cannot be reproduced by a scalar-relativistic treatment only. 相似文献
12.
In this paper the authors have applied the infinite-order two-component method (IOTC) to compute the valence and inner shell ionization potentials for the Ne, Ar, Kr, and Xe elements. The obtained results show the very good performance of the recently defined relativistic IOTC method. They also confirm the importance of the relativistic effects in the determination of the inner shell ionization potentials. 相似文献
13.
S. Hofstetter N. Grün W. Scheid 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,37(1):1-7
We have used a relativistic classical trajectory Monte Carlo (CTMC)-method to calculate cross sections for single and double ionization of helium by relativistic heavy ions. We compare our results with experimentally obtained cross sections. We comment on the limits of the validity of relativistic classical calculations. 相似文献
14.
15.
Pavel Neogrdy Vladimir Kell Miroslav Urban Andrzej J. Sadlej 《International journal of quantum chemistry》1997,63(2):557-565
The electron correlation and relativistic effects on ionization potentials and electron affinities of Cu, Ag, and Au are investigated in the framework of the coupled cluster method and different 1-component approximations to the relativistic Dirac-Coulomb Hamiltonian. The first-order perturbation approach based on the massvelocity and Darwin terms is found to be sufficiently accurate for Cu and Ag while it fails for Au. The spin-averaged Douglas-Kroll no-pair method gives excellent results for the studied atomic properties. The ionization potentials obtained within this method and the coupled cluster scheme for the electron correlation effects are 7.733(7.735) eV for Cu, 7.461(7.575) eV for Ag, and 9.123(9.225) eV for Au (experimental values given in parentheses). The calculated (experimental) electron affinity results for Cu, Ag, and Au are 1.236(1.226), 1.254(1.303), and 2.229(2.309) eV, respectively. There is a marked relativistic effect on both the ionization potential and electron affinity of Ag which sharply increases for Au while Cu exhibits only a little relativistic character. A similar pattern of relativistic effects is also observed for electric dipole polarizabilities of the coinage metal atoms and their ions. The coupled cluster dipole polarizabilities of the coinage metal atoms calculated in this article in the Douglas-Kroll no-pair formalism (Cu: 46.50 au; Ag: 52.46 au; Au: 36.06 au) are compared with our earlier data for their singly positive and singly negative ions. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 557–565, 1997 相似文献
16.
We applied the spin-free relativistic infinite-order two-component method to calculate the core-electron binding energies of different tautomeric structures of thio- and selenocytosine. The importance of relativistic effects in the ionization of 1s electrons was studied for selenocytosine. The present method provides a reasonably simple and reliable computational tool for calculating the core electron binding energies of molecules containing heavy atoms. The method can also be used for characterization of different tautomeric structures of nucleic acid basis. 相似文献
17.
George B. Bacskay 《Chemical physics》1980,48(1):21-38
The vertical valence ionization potentials of Ne, H2O and N2 have been calculated by Rayleigh-Schrödinger perturbation and configuration interaction methods. The calculations were carried out in the space of a single determinant reference state and its single and double excitations, using both the N and N - 1 electron Hartree-Fock orbitals as hole/particle bases. The perturbation series for the ion state were generally found to converge fairly slowly in the N electron Hartree-Fock (frozen) orbital basis, but considerably faster in the appropriate N - 1 electron RHF (relaxed) orbital basis. In certain cases, however, due to near-degeneracy effects, partial, and even complete, breakdown of the (non-degenerate) perturbation treatment was observed. The effects of higher excitations on the ionization potentials were estimated by the approximate coupled pair techniques CPA′ and CPA″ as well as by a Davidson type correction formula. The final, fully converged CPA″ results are generally in good agreement with those from PNO-CEPA and Green's function calculations as well as experiment. 相似文献
18.
Small-core ten-valence electron energy-consistent scalar- and two-component relativistic pseudopotentials for the alkaline-earth elements from Ca to Ra are presented. The accuracy and reliability of these pseudopotentials are discussed in terms of their ability to reproduce all-electron calculated and experimental dipole polarizabilities and ionization potentials. 相似文献
19.
Inhester L Burmeister CF Groenhof G Grubmüller H 《The Journal of chemical physics》2012,136(14):144304
The high intensity of free electron lasers opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules, radiation damage induced by absorption of high intense x-ray radiation is not yet fully understood. One of the striking effects which occurs under intense x-ray illumination is the creation of double core ionized molecules in considerable quantity. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From the MD trajectories, photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schro?dinger equations. These rates served to solve the master equations for the populations of the relevant electronic states. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were incoherently accumulated according to the obtained time-dependent populations, thus neglecting possible interference effects between different decay pathways. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint in the resulting electron emission spectra. The lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime. 相似文献
20.
An assortment of computer-generated, parallel-executable programs of ab initio electron-correlation methods has been fitted with the ability to use relativistic reference wave functions. This has been done on the basis of scalar relativistic and spin-orbit effective potentials and by allowing the computer-generated programs to handle complex-valued, spinless orbitals determined by these potentials. The electron-correlation methods that benefit from this extension are high-order coupled-cluster methods (up to quadruple excitation operators) for closed- and open-shell species, coupled-cluster methods for excited and ionized states (up to quadruples), second-order perturbation corrections to coupled-cluster methods (up to triples), high-order perturbation corrections to configuration-interaction singles, and active-space (multireference) coupled-cluster methods for the ground, excited, and ionized states (up to active-space quadruples). A subset of these methods is used jointly such that the dynamical correlation energies and scalar relativistic effects are computed by a lower-order electron-correlation method with more extensive basis sets and all-electron relativistic treatment, whereas the nondynamical correlation energies and spin-orbit effects are treated by a higher-order electron-correlation method with smaller basis sets and relativistic effective potentials. The authors demonstrate the utility and efficiency of this composite scheme in chemical simulation wherein the consideration of spin-orbit effects is essential: ionization energies of rare gases, spectroscopic constants of protonated rare gases, and photoelectron spectra of hydrogen halides. 相似文献