Vertically coupled quantum dots in the local spin-density functional theory

We have investigated the structure of double quantum dots vertically coupled at zero magnetic field within local spin-density functional theory. The dots are identical and have a finite width, and the whole system is axially symmetric. We first discuss the effect of thickness on the addition spectrum of one single dot. Next, we describe the structure of coupled dots as a function of the interdot distance for different electron numbers. Addition spectra, Hund's rule and molecular-type configurations are discussed. It is shown that self-interaction corrections to the density functional results do not play a very important role in the calculated addition spectra.Comment: Typeset using Revtex, 14 pages and 12 Postscript figures, to be published in Phys. Rev.

Far-infrared spectroscopy of nanoscopic InAs rings

We have employed time-dependent local-spin density theory to analyze the far-infrared transmission spectrum of InAs self-assembled nano-rings recently reported [A. Lorke et al, cond-mat/9908263 (1999)]. The overall agreement between theory and experiment is good, which on the one hand confirms that the experimental peaks indeed reflect the ring-like structure of the sample, and on the other hand, asseses the suitability of the theoretical method to describe such small nanostructures. The addition energies of one- and two-electron rings are also reported and compared with the corresponding capacitance spectra.Comment: Typeset using Revtex, 7 pages and 8 Postscript figure

Wave-vector dependence of spin and density multipole excitations in quantum dots

We have employed time-dependent local-spin density functional theory to analyze the multipole spin and charge density excitations in GaAs-AlGaAs quantum dots. The on-plane transferred momentum degree of freedom has been taken into account, and the wave-vector dependence of the excitations is discussed. In agreement with previous experiments, we have found that the energies of these modes do not depend on the transferred wave-vector, although their intensities do. Comparison with a recent resonant Raman scattering experiment [C. Sch\"uller et al, Phys. Rev. Lett {\bf 80}, 2673 (1998)] is made. This allows to identify the angular momentum of several of the observed modes as well as to reproduce their energies.Comment: 14 pages in REVTEX and 14 postscript figure

Wave-vector dependence of spin and density multipole excitations in quantum dots

We have employed time-dependent local-spin density functional theory to analyze the multipole spin and charge density excitations in GaAs-AlGaAs quantum dots. The on-plane transferred momentum degree of freedom has been taken into account, and the wave-vector dependence of the excitations is discussed. In agreement with previous experiments, we have found that the energies of these modes do not depend on the transferred wave-vector, although their intensities do. Comparison with a recent resonant Raman scattering experiment [C. Sch\"uller et al, Phys. Rev. Lett {\bf 80}, 2673 (1998)] is made. This allows to identify the angular momentum of several of the observed modes as well as to reproduce their energies.Comment: 14 pages in REVTEX and 14 postscript figure

Isomeric electronic states in concentric quantum rings

We show that polarized few-electron concentric double quantum rings display localized states that are the quantum analog of classical equilibrium ones. These states have very similar energies but fairly different angular momenta, constituting a new physical realization of the isomeric states found in nuclear and molecular physics. Their fingerprint is a very soft mode in the infrared-absorption spectrum at nearly the dipole excitation energy of a rigidly rotating N-electron molecule. The yrast line and the infrared-absorption spectrum are discussed for N=4 and 6 electron configurations

Vertically coupled quantum dots in the local spin-density functional theory

To be published in Phys. Rev. BConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Finding Conformational Transition Pathways from Discrete Molecular Dynamics Simulations

We present a new method for estimating pathways for conformational transitions in macromolecules from the use of discrete molecular dynamics and biasing techniques based on a combination of essential dynamics and Maxwell–Demon sampling techniques. The method can work with high efficiency at different levels of resolution, including the atomistic one, and can help to define initial pathways for further exploration by means of more accurate atomistic molecular dynamics simulations. The method is implemented in a freely available Web-based application accessible at http://mmb.irbbarcelona.org/MDdMD