Electronic structure of the ideal silicon vacancy by the muffin-tin green's function method

The muffin-tin Green's function method is applied to the ideal vacancy in silicon in the extended-charge single site approximation. The characteristics of the partially occupied gap state are found to be strongly dependent on the extent of the charge perturbation outside of the vacancy muffin-tin.     

Ti+2 impurity states in ZnSe by the green's function method

A generalization of the molecular multiple scattering method to potentials consisting of a muffin-tip potential plus a spherically symmetric potential is used in calculations of the electronic structure of titanium impurity in zinc selenide. The results are compared with that obtained by the usual multiple-scattering method and with available experimental data.     

On the semiclassical green's function in the energy-representation

We present a detailed discussion of the semiclassical approximation for the Green's function in the energy representation, G(qⁱ,q^j; E). In particular, we describe the way in which classical catastrophes influence the semiclassical approximation, and present a practical scheme to determine the phases with which the contributions due to the various classical trajectories enter the semiclassical result.     

Binary collision expansion and partial green's functions of Kadanoff-Baym

A new formula for the binary collision expansion of the unitary operator U (t₂, t₁) is proposed. The formula is applied to the expansion of the partial Green's functions of Kadanoff-Baym in powers of the correct binary scattering amplitude. It is shown that certain linked diagrams of left-multidentate structure should be taken into account. The duration of the binary collision is seen to play an important role in the rigorous formulation. Upon neglecting this duration, a useful approximation is found for the analysis of correlations on a macroscopic time scale.     

Geometric dependence of casimir energy and scalar green's functions

It is well known that the Casimir Energy depends on the geometry of the conducting cavity. In this note, scalar Green's functions are used to determine the Casimir energy's dependence on terms bilinear in the extrinsic curvatures of the cavity's surface, and thus to resolve the controversy over the Casimir energy's finiteness.     

Higher order field equations II; Limit properties of green's functions

In a previous paper wave propagation was studied according to a sixth-order partial differential equation involving a complex mass M. The corresponding Yang-Feldman integral equations (indicated as SM-YF-equations), were formulated using modified Green's functions G^M_R(x) and G^M_A(x), which then incorporate the partial differential equation together with certain boundary conditions. In this paper certain limit properties of these modified Green's functions are derived: (a) It is shown that for |M| → ∞ the Green's functions G^M_R(x) and G^M_A(x) approach the Green's functions Δ_R(x) and Δ_A(x) of the corresponding KG-equation (Klein-Gordon equation). (b) It is further shown that the asymptotic behaviour of G^M_A(x) and G^M_A(x) is the same as of Δ_R(x) and Δ_A(x) - and also the same as for D_R(x) and D_A(x) for t→ ± ∞, where D_R and D_A are the Green n's functions for the KG-equation with mass zero. It is essential to take limits in the sense of distribution theory in both cases (a) and (b). The property (b) indicates that the wave propagation properties of the SM-YF-equations, the KG-equation with finite mass and the KG-equation with mass zero are closely related in an asymptotic sense.     

A classical green's function approach to vibrational spectra of biopolymers

Classical green's function methods can be used to calculate the spectra of large molecules by essentially putting together the spectra of smaller parts. The methods are useful where the parts are connected by few valence bonds.     

Functional approach to the parametric derivatives of renormalized green's functions with multiple insertions

Functional derivation of formulae for parametric derivatives of renormalized Green's functions with multiple insertions of composite operators is presented. An application to the derivative with respect to the ultraviolet cutoff in the Pauli–Villars regularized ?⁴₄ theory is given.     

Dissociative ionization of molecules in intense laser fields

Accurate and efficient grid based techniques for the solution of the time-dependent Schrödinger equation for few-electron diatomic molecules irradiated by intense, ultrashort laser pulses are described. These are based on hybrid finite-difference, Lagrange mesh techniques. The methods are applied in three scenarios, namely H₂ ⁺ with fixed internuclear separation, H₂ ⁺ with vibrating nuclei and H₂ with fixed internuclear separation and illustrative results presented.Received: 19 November 2002, Published online: 24 April 2003PACS: 02.60.Cb Numerical simulation; solution of equations - 02.70.Bf Finite-difference methods - 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 33.80.-b Photon interactions with molecules     

Saturated ionization of fullerenes in intense laser fields

We investigate the ionization of icosahedral fullerenes (C20, C60, C80, and C180) in an intense laser pulse using the S-matrix theory. The results obtained are in excellent agreement with the recent observations of unexpectedly high saturation intensities of the Buckminster fullerene and its multiply charged ions. Our analysis strongly suggests that the related phenomenon of suppressed ionization of these complex fullerenes is due to the finite cage size and the "multislit" interference effect between partial waves emitted from the different nuclei rather than to a dynamical multielectron polarization effect.     

Infra-red asymptotic behaviour of the one-fermion green's function in a scalar model with isospin

In a theory where massive fermions interact with a massless scalar field of isospin 1, the behaviour of the one-fermion Green's function is found to differ from the free Green's function by a factor $\text{(1 ? (2g}{}^2\text{/π}{}^2\text{)1}\text{n}\text{m|x ? y|)}{}^{\mathrm{<mtext>?</mtext><mtext>3</mtext><mtext>8</mtext>}}$, in the limit of large separation |x ? y|.     

Selection rules for atom multiphoton ionization by intense light in a non-perturbative theory

Using a non-pertubative theoretical analysis we establish the selection rules for the multiphoton ionization effect in hydrogen-like atoms by intense linearly and circularly polarized light, alternatively. No approximations are carried out during these calculations and the obtained results are more general than those obtained to date.     

Interpretation of the photoelectron spectrum of norbornadiene: A green's function approach

The ionization potentials of norbornadiene are calculated by an ab initio many-body Green's function method. The photoelectron spectrum as recorded by Heilbronner and co-workers can thus be interpreted. The first two ionization potentials are 5b₂ (π) and 7a₁ (π) (with increasing binding energy) in agreement with previous investigations.     

Effect of electron excitation in nonsequential double ionization by intense laser fields

We study the double ionization process of atoms in intense laser fields. The momentum distributions of the correlated electrons are calculated. Contrary to the general expectation, we show an increasing proportion of the electrons ionized via excitation with the increasing laser intensity. These electrons generally have small energy thus they concentratedly distribute on the central region of the momentum diagram. Consequently, the central part of the momentum diagram becomes more notable in higher intensity laser fields. Further study suggests that this phenomenon is general in double ionization.     

Resonant interaction between intense electromagnetic waves during ionization of an atom

Resonant interaction through the continuum between two intense electromagnetic waves of different frequencies during ionization of an atom is considered. A general solution of the problem is found by using a procedure based on the application of the Laplace transform to the equations for the time-dependent amplitudes of the probability. When one of the EM waves is considerably weaker than the other, the dynamics of the absorption of light by an atom are investigated, and a final value for the ionization probability in the illumination region is found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 63–70, January, 1978.     

The equations of motion for green's functions and superconductivity solutions in particle physics

Three quantum field models are treated in a unified manner by using the method familiar from statistical many-body theory of solving the equations of motion for the Green functions in a particle number representation, with the following results: While the Nambu model does undergo dynamical symmetry breaking in its (1 + 1) dimensional version, it fails to do so in the original (3 + 1) dimensional case. For spinor QED, we get a critical value of the coupling parameter $\text{α}{}_{\mathrm{<mtext>c</mtext>}}\text{≡}\text{e}{}_{\mathrm{<mtext>c</mtext>}}{}^2\text{4π}\text{= 2π}$, above which the model becomes unstable.     

Above-threshold ionization of hydrogen atom in chirped laser fields

Above-threshold ionization(ATI) of a hydrogen atom exposed to chirped laser fields is investigated theoretically by solving the time-dependent Schr o¨dinger equation. By comparing the energy spectra, the two-dimensional momentum spectra, and the angular distributions of photoelectron for the laser pulses with different chirp rates, we show a very clear chirp dependence both in the multiphoton and tunneling ionization processes but no chirp dependence in the single-photon ionization. We find that the chirp dependence in the multiphoton ionization based ATI can be attributed to the excited bound states. In the single-photon and tunneling ionization regimes, the electron can be removed directly from the ground state and thus the excited states may not be very important. It indicates that the chirp dependence in the tunneling ionization based ATI processes is mainly due to the laser pulses with different chirp rates.