A resolvent expansion theorem for the Fourier transform of the retarded Green function and its application to the absorption bandshape of chromophore aggregates

A resolvent expansion theorem is developed for the Fourier transform of the retarded Green function. The resolvent expansion theorem coupled with a decorrelation approximation for a statistical average over the vibrational sublevels of the electronic ground state is applied to a theoretical formulation of the averaged Green function of chromophore aggregates. Consequently, thermal and static effects upon the aggregate's absorption bandshape are incorporated in terms of the correction shift of the individual chromophore's bandshapes. The utility of the theoretical formulation is shown by an illustrative calculation of the absorption bandshape of a model dimer.     

Exciton dynamics in molecular crystals from line shape analysis. The use of spectral moments and correlation functions

A method for elucidating exciton dynamics from the profile of ω?_i(ω) is developed and illustrated by using anthracene crystal reflectance data. From the Green's function for the exciton-phonon system, terms contributing to each spectral moment are rendered explicit. The Green's function is related to certain correlation functions which together with the spectral moments are evaluated from the spectral data.     

The one-particle green's function: The minimal basis set description of the two-electron bond

The ionization potential (IP), electron affinity (EA), one-matrix and correlation energy of a two-electron chemical bond are calculated in a minimal basis set using one-particle, many-body Green's function theory. Results obtained using the second-order self-energy (Σ) and higher-order Σ's proposed by (1) Pickup and Goscinski, (2) Tsui and Freed, (3) Simons and Smith are compared with each other and with the exact values in the basis. The relationship between these methods and with configuration interaction is discussed and the consequences of making approximations in the context of Green's function theory are clarified.     

A combined SAMO-ZDO method for the evaluation of ionization potentials

A scheme for the ab initio calculation of vertical ionization potentials without the necessity to compute two-electron repulsion integrals is discussed. The method employs the simulated ab initio molecular orbital (SAMO) method to generate Koopman's theorem eigenvalues. These are then corrected for the change in relaxation and correlation effects due to ionization by a Green's function perturbation scheme, in which all necessary integrals are evaluated using the zero differential overlap (ZDO) approximations, in this case the complete neglect of differential overlap (CNDO) method.     

The He(II) photoelectron spectra of the fluorosubstituted ethylenes and their analysis by the Green's function method

The 30.4 nm He(II) photoelectron spectra of the fluorosubstituted ethylenes have been recorded. The assignment of all main bands is obtained from many-body Green's function calculations. The results from the semi-empirical HAM/3 method lead to a nearly identical assignment. For the mono- and difluoroethylenes, an unambiguous interpretation of the spectra can be established from empirical considerations alone. The set of spectra has been reexamined with respect to the “perfluoro-effect” rules. Also discussed are the ionisation energies as a function of the geminal FCF bonding angle and the similarity of the spectra of the cis and trans isomers of 1,2-difluoroethylene. Additional weak bands were detected in the energy region 21–24 eV in all spectra and were attributed to “shake-up” transitions on the basis of 2ph-Tamm-Dancoff Green's function calculations. The orbital model of ionisation breaks down for the ionisation out of the F(2s) and C(2s) orbitals in general. The calculations reveal a charge transfer character of the excitations accompanying ionisation from the C(2s) orbitals.     

Bound state properties of H2 by the many-body green's function method

The Dyson equation for the one-electron Green's function is solved through approximating the optical potential by means of the functional derivative method. The results for the H₂ molecule, including ground state energy and the first six vertical ionization energies, are discussed and compared with experimental values.     

Tight-binding cluster Bethe lattice model studies of chemisorption

The surface Green's function which is used in model calculations for chemisorption systems has been approximated by the tight-binding cluster Bethe lattice model (TBCBLM). It is shown that for chemisorption of a single-orbital atom on a simple cubic lattice this model yields results in good agreement with Einstein and Schríeffer's results. The effects of cluster size on the chemisorption properties are explored.     

On the controversial assignment of the ionization potentials of formaldehyde

The Hartree-Fock calculations and the SCF Xα scattered-wave method using overlapping spheres predict a different ordering of the ionization potentials of formaldehyde. To clarify the problem a Green's function approach including many-body effects is used. The calculated ionization potentials as well as the vibrational structure of the bands agree well with experiment. We conclude the Hartree-Fock assignment to be the correct one.     

Green's function semiclassical quantization of non-closed quasiperiodic classical trajectories

A semiclassical quantization procedure is introduced within the Green's function formalism for non-closed quasiperiodic trajectories which have previously defied quantization with this formalism. The results are interpreted in terms of the uncertainty principle and lead to conjectures concerning the semiclassical quantization of ergodic trajectories.     

Double-ionization auger satellites obtained by the green's function method

A three-particle Green's function approach is used to obtain triple ionization potentials and double-ionization Auger satellites. Electron correlation is included beyond reorganization. Transition energies and intensities are calculated for the hydrogen fluoride molecule. The assignment of the 629 eV structure to double-ionization satellites is confirmed.     

Calculation of the HeI photoelectron spectrum of CS including satellite lines

The ionization potentials and the vibrational structure in the photoelectron spectrum of the CS molecule aer calculated using a Green's function approach. The inclusion of many-body corrections to Koopmans' theorem is necessary in order to obtain the correct ordering of the first two ionization potentials. In contrast to previous interpretations of the spectrum the third band has to be assigned to a shake-up line and the fourth to the 6σ orbital. The calculated vibrational structure is in good agreement with experiment and corroborates this assignment.     

Green's function calculations on the Auger spectra of CO

The Auger spectra of carbon monoxide have been calculated by the Green's function method and the unsolved assignment problems have been studied. Electron correlation plays an important role in all parts of the spectra. The results favour the assignment of the 250 eV peak in the C (KVV) spectrum as mainly 4σ¹5σ¹.     

Hole-mixing effects in the ionization of some unsaturated oxo-compounds

The He(II) photoelectron spectra of acrolein, propynal, propynol and propiolic acid are interpreted with the aid of ab initio many-body Green's function calculations in the outer and inner valence region. Koopmans' approximation fails to supply the correct ordering of electronic states in the radical cation if the lone pair orbital on the oxygen atom is of a′ symmetry. In the case of propynal the ordering of two ionic states o f equal symmetry is interchanged with respect to the Koopmans' orderin. A strong mixing of hole configurations occurs for outer valence states of propynol and propiolic acid. The implications of this mixing are briefly discussed.     

Ionization of CH4 and some fluoromethanes: a green's function study and an (e,2e) spectroscopic investigation

A Green's function study and an (e,2e) spectral investigation have been performed on CH₄ and some of its fluoro derivatives. The satellite structures and the breakdown of the orbital picture for inner valence shells are discussed.     

Dye laser excitation of the fluorosulfate radical. Totally symmetric upper state fundamentals

Upper state vibronic levels associated with totally symmetric fundamentals of the fluorosulfate radical were populated by means of dye laser excitation. The analysis of the resulting fluorescence confirmed the assignment of these levels. Theoretical intensities using the Green's function approach to vibronic coupling were calculated and compared to the experimental values.     

Ionization of fluoromethanes: CHF3 and CF4. A Greens̀ function study and an (e, 2e) spectroscopic investigation

A Green's function study has been performed on CHF₃ and CF₄. Theoretical results are compared with (e 2e) spectral data. Previous assignment of valence-shell orbitals is confirmed and a splitting of the innermost ionizations over many shake-up terms in experimental and theoretical results on both molecules.     

AB-initio effective potentials derived from many-body green's function theory: Application to Li

The many-body Green's function technique, developed by Schneider, Taylor and Yaris for electron scattering problems, is applied to the calculation of ab-initio effective potentials (pseudo-potentials) in atoms and molecules. Computational results on the ionization potentials, excitation energies and bound-bound oscillator strengths in lithium show quantitative agreement with experiment and contain all the heuristically expected physical effects.     

Green's function calculations of ground-state correlation energies

A computationally convenient and numerically stable procedure is reported for the direct calculation of ground-state correlation energies employing one-particle Green's functions.     

Strong correlation effects in the ionisation of CS2

The Hell photoelectron spectrum of CS₂ is presented. This spectrum is investigated by two different Green's function calculations. For the outer valence region the origin and assignment of satellite lines of significant intensity is clarified. Strong final state correlation effects are found for the inner valence region showing the so-called breakdown of single-particle picture of ionisation.     

Elementary derivation of the nth moment of magnetic resonance absorption lines from sum rules for two time retarded green's functions

This paper presents an elementary derivation for the nth moment of magnetic resonance linear response lineshape using sum rules for two time retarded Green's functions. The results can be particularized to the high-temperature regime where van Vleck's well-known relations are obtained.