Search Results - (Author, Cooperation:G. Vignale)

2011-06-04

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

0038-1098

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0038-1098

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0038-1098

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0375-9601

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0378-4363

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

1434-6036

Springer Online Journal Archives 1860-2000

Physics

Abstract The many-electron Green's function scheme is combined with theories for substitutional disorder, in particular the coherent potential approximation (CPA). Emphasis is placed on both insulating and metallic solids, for which the homogeneous electron gas description is not valid. To this a new set of formally exact equations is derived for the calculation of the disorder and Coulomb contributions to the electron self-energy. One of the equations, determining the disorder contribution as a functional of the average self-consistent propagatorG, can be treated by standard methods such as the CPA. The other equation, determining the Coulomb contribution ∑ c as a functional ofG is solved at three levels of approximation: (i) At the simplest level, disorder-induced correlations are neglected, resulting in ∑ c [G]=∑0[G], where ∑0 is the Coulomb self-energy functional. It is argued that this is already a reasonable approximation in an insulator. (ii) At the second level, disorder-induced correlations within the particle-hole propagators are taken into account in the expression for ∑ c . This approximation is particularly relevant for metals, since it generates the diffusion pole. (iii) At the third level, the correlations responsible for the Altshuler-Aronov anomalies observed in the density of states of disordered metals are additionally incorporated. From the self-energy, expressions for the linear response to an electromagnetic field are derived. A practical trunction to first order in the screened Coulomb interaction is suggested. A comparison with some previously advanced theories, in particular the Korringa-Kohn-Rostoker-CPA (KKR-CPA), is made.

Electronic Resource

0392-6737

Collective excitations (including plasmons and other chargedensity excitations) ; General theories and computational techniques (including manybody perturbation theory, density-functional theory, atomic sphere approximation methods, Fourier decomposition methods, etc.) ; Charge-density-wave systems

Springer Online Journal Archives 1860-2000

Physics

Summary The dispersion relations and the shear modulus of the 2D Wigner crystal (WC) in the presence of a strong magnetic field are evaluated using a density functional method which includes the effect of electronic correlations. Comparison is made with previous theoretical results on the magnetophonons and the shear modulus. The effect of correlation on the stability of the crystal is discussed.

Electronic Resource

0392-6737

Springer Online Journal Archives 1860-2000

Physics

Riassunto Si calcola la probabilità di transizione a due fotoni tra gli stati 11 S e 21 S dell’He atomico nell’approssimazione a elettroni indipendenti, usando semplici funzioni d’onda. I risultati ottenuti con l’interazione della formae E·r e con l’interazione della forma —(e/mc)A·p differiscono per meno del 20%, ma si mostra che la prima forma conduce a risultati piú attendibili. Si calcolano i valori dei coefficienti di assorbimento con luce laser di varia frequenza, e si suggerisce la possibilità di esperimenti in cui si utilizzi luce laser e radiazione di sincrotrone. La relazione di Einstein tra assorbimento ed emissione spontanea può essere estesa ai processi a due fotoni e da essa si calcola il tempo naturale di vita dello stato 21 S dell’elio, per il quale si ottiene il valore di ∼25 ms, in ragionevole accordo con risultati sperimentali ed altri risultati teorici.

Резюме Рычисляется вероятность двухфотонного перехода между состояниями 11 S и 21 S в атоме He в одно-злектронном приближении, используя простые приближенные волновые функции. Результаты, полученные дляe E·r взаимодействия и для—(e/mc)A·p взаимодействия, отличаются менее, чем на 20%, но первая форма взаимодействия дает более непротиворечивые результаты. Проводятся вычисления коэффициентов поглошения для лазерного излучения различных частот. Предлагаются эксперименты с исполязованием синхротронного излучения и лазерного пучка. Соотношение Эйнштейна между поглощением и спонтанным излучением может быть обобщено на случай двухфотонных процессов. Вычисляется естественное время жнзни 21 S состояния He, которое составляет ∼25 мс, что находится в разумном согласии с экспериментом и другими вычислениями.

Summary The two-photon transition probability between the 11 S and the 21 S states of atomic He has been computed in the one-electron approximation by using simple approximate wave functions. The results with thee E·r interaction and with the— (e/mc)A·p interaction differ by less than 20%, but the former is shown to give more consistent results. The values of the absorption coefficients for a laser radiation of varying frequency are shown to be experimentally accessible and experiments are suggested with sinchrotron radiation and a laser beam. The Einstein relation between absorption and spontaneous emission can be extended to two-photon processes and the natural lifetime of the 21 S-state of He is computed and found to be ∼25 ms, in reasonable agreement with experiment and with other calculations.

Electronic Resource

1434-6036

Springer Online Journal Archives 1860-2000

Physics

Abstract A new set of self-consistent equations is proposed for the calculation of the disorder and Coulomb contributions to the electron self-energy and the electron-hole interaction in a many-electron system in the presence of a site-diagonal random potential. The treatment of the disorder is along the lines of the coherent-potential approximation. An explicit expression for the Coulomb self-energy is derived within the time-dependent screened Hartree-Fock approximation. Some possible applications of the formalism to the formation of a Coulomb gap in a doped semiconductor and to electron-hole interaction effects in the optical spectra of alloy semiconductor systems are discussed.

Electronic Resource

1434-6036

Springer Online Journal Archives 1860-2000

Physics

Abstract The previously developed theory [1] for interacting electrons in a not necessarily weak random potential is applied to a tight-binding model of a cubic metal alloy with binary diagonal disorder. On the basis of this model, the effective Coulomb self-energy ∑ c is calculated as a function of both momentum and energy. It is shown that that the effects of the band structure on the Altshuler-Aronov anomalies in the density of states can be incorporated in a renormalization of physical parameters like the diffusion constantD and the triplet interaction constant $$\mathfrak{F}$$ . This result is shown to follow from a non-trivial cancellation of band-structure dependent terms, which is only attained when ternary correlations and exclusion corrections are properly included in the coherent potential approximation-based expression for the Coulomb self-energy. The enhanced inelastic lifetime of electrons is also considered and the familiarT −3/2 behavior, with band structure effects absorbed in the definition ofD, is obtained.

Electronic Resource

0020-7608

Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

We formulate the current-density functional theory for systems in arbitrarily strong magnetic fields. A set of self-consistent equations comparable to the Kohn-Sham equations for ordinary density functional theory is derived, and proved to be gauge-invariant and to satisfy the continuity equation. These equations of Vignale and Rasolt involve the gauge field corresponding to the external magnetic field as well as a new gauge field generated entirely from the many-body interactions. We next extend this gauge theory (following Rasolt and Vignale) to a lattice Lagrangian believed to be appropriate to a tight-binding Hamiltonian in the presence of an external magnetic field. We finally examine the nature of the ground state of a strongly nonuniform electron gas in the presence of this many-body, self-induced gauge field. © 1992 John Wiley & Sons, Inc.

1 Ill.

Electronic Resource