| 1. |
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Hedin, Lars, et al.
(författare)
-
Effects of Electron-Electron and Electron-Phonon Interactions on the One-Electron States of Solids
- 1969
-
Ingår i: Solid State Physics. - 9780126077230 ; 23, s. 1-181
-
Bokkapitel (refereegranskat)abstract
- Publisher Summary: This chapter discusses two major developments that have taken place over the past decade. First is the enormous wealth of energy band calculations that have had tremendous success in explaining the properties of specific solids, but in which the connection with first principles is not always apparent. Second is the spectacular progress of many-body theory applied to the solid state that has given a number of new results, although often of a rather general and formal nature, such as to provide the justification and a formal basis for a one-electron theory. The electron gas problem is treated in some detail here. The problem of the crystal potential is given due attention. It discusses the potential from the ion cores as well as from the valence electrons, and suggests schemes that incorporate essential exchange and correlation effects for the valence electrons. An energy band calculation that properly includes the effects of exchange and correlation describes the elementary excitations called quasi particles. Quasi-particle properties are usually discussed using the remarkable Landau theory of the Fermi liquid. This chapter gives a brief presentation of the theory and reviews the present status of calculations of the Fermi liquid parameters and how they are determined from experiments.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Hedin, Lars, et al.
(författare)
-
Explicit local exchange-correlation potentials
- 1971
-
Ingår i: Journal of Physics C: Solid State Physics. - 0022-3719. ; 4:14, s. 2064-2083
-
Tidskriftsartikel (refereegranskat)abstract
- The possibilities of the Hohenberg-Kohn-Sham local density theory are explored in view of recent advances in the theory of the interacting electron gas. The authors discuss and provide numerical data for the effective exchange-correlation potentials μxc for ground state problems and Vxc for excitation spectra. The potential μxc(r) is written as a factor β(ρ(r)), which depends on the local density ρ(r), times the Kohn-Sham-Gaspar potential μx=-e2kF/π. The factor β, which is represented by a simple analytical formula, varies between 1 for very high densities and about 1.5 for very low densities, where μxc thus approaches the Slater approximation. The potential Vxc is given in the form of a table. The explicit predictions of the approximate theories are mapped in their linearized versions. The theory is also developed for the case when the ion cores are treated separately, and the local density approximation is applied only to the valence electrons.
|
|
| 10. |
- Hedin, Lars, et al.
(författare)
-
Local exchange-correlation potentials
- 1971
-
Ingår i: Solid State Communications. - : Elsevier BV. - 1879-2766 .- 0038-1098. ; 9:9, s. 537-541
-
Tidskriftsartikel (refereegranskat)abstract
- Recent advances in the many-body theory of electrons in solids and in the theory of the interacting electron gas are used to construct explicit local effective potentials which incorporate the effects of correlation and exchange. For ground state properties we consider the scheme by Hohenberg, Kohn and Sham and provide data for the effective potential μxc. For excitation energies the corresponding potential Vxc is obtained from the self-energy of an electron gas and numerical data are provided for the construction of Vxc.
|
|
| 11. |
- Hedin, Lars, et al.
(författare)
-
Many-body effects
- 1974
-
Ingår i: X-ray spectroscopy. ; , s. 226-226
-
Bokkapitel (refereegranskat)abstract
|
|
| 12. |
|
|
| 13. |
- Hedin, Lars
(författare)
-
Many-body effects in soft X-ray emission in metals
- 1967
-
Ingår i: Solid State Communications. - : Elsevier BV. - 1879-2766 .- 0038-1098. ; 5:6, s. 451-454
-
Tidskriftsartikel (refereegranskat)abstract
- Soft X-ray emission in metals is treated, taking many-body effects and the electron-hole attraction into account. An appropriate connection with electron gas results is made. The structure in the low energy tail due to many-body effects are discussed, and the existence of a new critical point is suggested.
|
|
| 14. |
|
|
| 15. |
- Hedin, Lars, et al.
(författare)
-
MANY-BODY EFFECTS ON DEEP LEVEL SPECTRA OF METALS
- 1978
-
Ingår i: Le Journale de Physique Colloques. ; C4, s. 11-103
-
Konferensbidrag (refereegranskat)abstract
- Many-body effects in metals due to a change in the core electron occupation number appear in a large number of spectroscopies. The possible importance of the core hole has been realized and discussed for a very long time. Mahan's idea of excitons in metals gave the topic strong stimulus. First the interest was focused on threshold singularities in simple metals. The topic was thoroughly discussed in Mahan's 1974 review and declared solved and completed. This declaration was strongly challenged by Dow and collaborators. This has led to a deeper and more detailed understanding. In particular the importance of static core hole effects, of phonons, of electron bandstructure, of exchange coupling (the Onodera effect) and of spindependent phaseshifts has been realized. Thus the longstanding puzzle of the lithium edge now seems to have found its solution in terms of phonons and bandstructure and not in the MND-effect - the broad emission edge can be explained by incomplete phonon relaxation and the broad absorption edge by the one-electron density of states.
|
|
| 16. |
- Hedin, Lars
(författare)
-
New Method for Calculating the One-Particle Green's Function with Application to the Electron-Gas Problem
- 1965
-
Ingår i: Physical Review series I. - 0031-899X. ; 139:3A, s. 796-823
-
Tidskriftsartikel (refereegranskat)abstract
- A set of successively more accurate self-consistent equations for the one-electron Green's function have been derived. They correspond to an expansion in a screened potential rather than the bare Coulomb potential. The first equation is adequate for many purposes. Each equation follows from the demand that a corresponding expression for the total energy be stationary with respect to variations in the Green's function. The main information to be obtained, besides the total energy, is one-particle-like excitation spectra, i.e., spectra characterized by the quantum numbers of a single particle. This includes the low-excitation spectra in metals as well as configurations in atoms, molecules, and solids with one electron outside or one electron missing from a closed-shell structure. In the latter cases we obtain an approximate description by a modified Hartree-Fock equation involving a "Coulomb hole" and a static screened potential in the exchange term. As an example, spectra of some atoms are discussed. To investigate the convergence of successive approximations for the Green's function, extensive calculations have been made for the electron gas at a range of metallic densities. The results are expressed in terms of quasiparticle energies E(k) and quasiparticle interactions f(k, k′). The very first approximation gives a good value for the magnitude of E(k). To estimate the derivative of E(k) we need both the first- and the second-order terms. The derivative, and thus the specific heat, is found to differ from the free-particle value by only a few percent. Our correction to the specific heat keeps the same sign down to the lowest alkali-metal densities, and is smaller than those obtained recently by Silverstein and by Rice. Our results for the paramagnetic susceptibility are unreliable in the alkali-metal-density region owing to poor convergence of the expansion for f. Besides the proof of a modified Luttinger-Ward-Klein variational principle and a related self-consistency idea, there is not much new in principle in this paper. The emphasis is on the development of a numerically manageable approximation scheme.
|
|
| 17. |
- Hedin, Lars, et al.
(författare)
-
New structure in the single-particle spectrum of an electron gas
- 1967
-
Ingår i: Solid State Communications. - : Elsevier BV. - 1879-2766 .- 0038-1098. ; 5:4, s. 237-239
-
Tidskriftsartikel (refereegranskat)abstract
- Calculations of the one-electron Green's function give a single-particle spectrum where, besides the usual quasi-particles, a new peak of appreciable strength appears which corresponds to an electron coupled to real plasmons.
|
|
| 18. |
- Hedin, Lars, et al.
(författare)
-
ON LOCAL DENSITY SCHEMES
- 1972
-
Ingår i: Le Journale de Physique Colloques. ; C3:5-6, s. 73-81
-
Konferensbidrag (refereegranskat)abstract
- This paper summarizes recent results how to obtain approximate one-electron potentials describing exchange and correlation which depend on the local electron density. Following the lines given by Hohenberg, Kohn and Sham explicit results are given in two versions of the theory; one to describe ground state properties and one for excitation energies. The extension to spin polarized systems is discussed and some new results are presented. The paper also summarizes recent results about the linear response properties and comments on the role of the non-locality of the self-energy.
|
|
| 19. |
- Hedin, Lars, et al.
(författare)
-
On temperature broadening in X-ray spectra of metals
- 1977
-
Ingår i: Journal of Physics F: Metal Physics. - 0305-4608. ; 7:7, s. 1339-1348
-
Tidskriftsartikel (refereegranskat)abstract
- Calculates the full width at half maximum (FWHM) of the phonon broadening function for Li, Na, K and Al at different temperatures. A theory is used which employs the ionic pseudopotential, rather than, as in Bergersen et al's (1971) theory, a bare Coulomb potential. Despite the fact that a pseudopotential in a general sense is weaker than a Coulomb potential the authors find that the former gives considerably larger FWHM's, e.g. in Li at T=0 the FWHM becomes more that doubled. They also discuss other broadening effects and conclude that their results are consistent with recent experimental data presented by Baer et al. (1976).
|
|
| 20. |
- Hedin, Lars, et al.
(författare)
-
On the single-particle spectrum of an interacting electron gas
- 1967
-
Ingår i: [Host publication title missing]. - : Wiley. ; 1, s. 237-237
-
Konferensbidrag (refereegranskat)abstract
- n the many-body theory of conduction electrons in a metal the single-particle spectrum is described not simply by the energy versus momentum relation as in band theory but by a function that describes the actual shape of the spectrum for a given momentum and has an appreciable spread in energy. Calculations of the spectral strength function for electrons in a uniform electron gas are described, where, besides the usual quasi-particle peak and a broad background, a new peak of appreciable strength appears for small momenta. The new excitation corresponds to a coupled mode of an electron and real plasmons. It has a strong effect on the energy distribution of electrons in the system. The effects should show up only in certain types of experiments that depend on the energy spectrum in the region where the new mode occurs.
|
|
| 21. |
|
|
| 22. |
- Hedin, Lars, et al.
(författare)
-
Polarization corrections to core levels
- 1969
-
Ingår i: Journal of Physics B: Atomic and Molecular Physics. - : IOP Publishing. - 0022-3700. ; 2:12
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical predictions for ionization energies of inner core electrons generally come out much more accurately by taking the difference between the total energies of two self-consistent Hartree-Fock calculations than by using Koopmans' theorem. For the outer core electrons, on the other hand, little or no improvement over Koopmans' theorem is obtained from a `ΔSCF method'. We show here that the difference between the results from the ΔSCF method and from Koopmans' theorem can be expressed in terms of a polarization potential. A simple physical argument can then be made as well as a comparison with second-order perturbation theory, which both show why the ΔSCF method should give good results for inner core levels but not necessarily for outer core levels. The formulation in terms of a polarization potential allows a systematic discussion and an easy calculation of chemical shifts in core levels. We find that the core electrons serve as probes on the charge density and the polarizability of the valence electron system. As numerical examples, results are given for ions, atoms and metals of sodium and potassium. The limitations and possible extensions of the theory are discussed.
|
|
| 23. |
|
|
| 24. |
- von Barth, Ulf, et al.
(författare)
-
A local exchange-correlation potential for the spin polarized case: I
- 1972
-
Ingår i: Journal of Physics C: Solid State Physics. ; 5:13, s. 1629-1642
-
Tidskriftsartikel (refereegranskat)abstract
- The local density theory is developed by Hohenberg, Kohn and Sham is extended to the spin polarized case. A spin dependent one- electron potential pertinent to ground state properties is obtained from calculations of the total energy per electron made with a `bubble' (or random phase) type of dielectric function. The potential is found to be well represented by an analytic expression corresponding to a shifted and rescaled spin dependent Slater potential. To test this potential the momentum dependent spin susceptibility of an electron gas is calculated. The results compare favourably with available information from other calculations and from experiment. The potential obtained in this paper should be useful for split band calculations of magnetic materials.
|
|
| 25. |
- von Barth, Ulf, et al.
(författare)
-
Correlated crystal potentials in band structure calculations
- 1974
-
Ingår i: Il Nouvo Cimento B. ; 23:1, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- The authors give a critical discussion of different current band structure schemes and their relaxation to experiment. They then discuss the connections, exact and approximate, that exist between the electron self-energy and experiment, considering in particular optical absorption and photoemission. Different computationally feasible approximation schemes based on a dynamic generalization of the nonlocal Hartree-Fock exchange potential are considered.
|
|
