Biomedical subjects

G Vignale

Publications and source records attributed to G Vignale.

At least 19 recordsLinked to original sources

PubMed2003

Solving the ultranonlocality problem in time-dependent spin-density-functional theory.

It has been known for some time that the exchange-correlation potential in time-dependent density-functional theory is an intrinsically nonlocal functional of the density as soon as one goes beyond the adiabatic approximation. In this paper we show that a much more severe nonlocality problem, with a completely different physical origin, plagues the exchange-correlation potentials in time-dependent spin-density functional theory. We show how the use of the spin current density as a basic variable solves this problem, and we provide an explicit local expression for the exchange-correlation fields as functionals of the spin currents.

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PubMed2002

Nonlinear spin-polarized transport through a ferromagnetic domain wall.

A domain wall separating two oppositely magnetized regions in a ferromagnetic semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V characteristics similar to those of a p-n diode. We study these characteristics as functions of wall width and temperature. As the width increases or the temperature decreases, direct tunneling between the majority spin bands reduces the effectiveness of the diode. This has important implications for the zero-field quenched resistance of magnetic semiconductors and for the design of a recently proposed spin transistor.

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PubMed2001

Spin currents and spin dynamics in time-dependent density-functional theory.

We derive and analyze the equation of motion for the spin degrees of freedom within time-dependent spin-density-functional theory (TD-SDFT). The results are (i) a prescription for obtaining many-body corrections to the single-particle spin currents from the Kohn-Sham equation of TD-SDFT, (ii) the existence of an exchange-correlation (xc) torque within TD-SDFT, (iii) a prescription for calculating, from TD-SDFT, the torque exerted by spin currents on the spin magnetization, (iv) a novel exact constraint on approximate xc functionals, and (v) the discovery of serious deficiencies of popular approximations to TD-SDFT when applied to spin dynamics.

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PubMed2001

Theory of the linewidth of intersubband plasmons in quantum wells.

Intersubband (ISB) plasmons in remotely doped wide quantum wells acquire a linewidth even at zero temperature and in-plane wave vector q(parallel) = 0 by a combination of intrinsic (electron-electron interaction) and extrinsic effects (impurities and interface roughness). We present a quantitatively accurate theory of the linewidth that treats both effects on equal footing and from first principles by a combination of time-dependent density-functional theory with the memory function formalism. Comparison with recent optical absorption experiments shows that the ISB plasmon linewidth has a significant contribution from electron-electron interaction, and is only weakly related to the mobility.

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PubMed2001

Nonuniqueness of the potentials of spin-density-functional theory.

It is shown that, contrary to widely held beliefs, the potentials of spin-density-functional theory (SDFT) are not unique functionals of the spin densities. Explicit examples of distinct sets of potentials with the same ground-state densities are constructed. These findings imply that the zero-temperature exchange-correlation energy is not always a differentiable functional of the spin density. As a consequence, various types of applications of SDFT must be critically reexamined.

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PubMed1996