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Showing papers on "Electronic structure published in 1995"


Journal ArticleDOI
TL;DR: In this paper, the strain distribution in and around pyramidal InAs/GaAs quantum dots (QD's) on a thin wetting layer fabricated recently with molecular-beam epitaxy, is simulated numerically.
Abstract: The strain distribution in and around pyramidal InAs/GaAs quantum dots (QD's) on a thin wetting layer fabricated recently with molecular-beam epitaxy, is simulated numerically. For comparison analytical solutions for the strain distribution in and around a pseudomorphic slab, cylinder, and sphere are given for isotropic materials, representing a guideline for the understanding of strain distribution in two-, one-, and zero-dimensional pseudomorphic nanostructures. For the pyramidal dots we find that the hydrostatic strain is mostly confined in the QD; in contrast part of the anisotropic strain is transferred from the QD into the barrier. The optical-phonon energies in the QD are estimated and agree perfectly with recent experimental findings. From the variation of the strain tensor the local band-gap modification is calculated. Piezoelectric effects are additionally taken into account. The three-dimensional effective-mass single-particle Schr\"odinger equation is solved for electrons and holes using the realistic confinement potentials. Since the QD's are in the strong confinement regime, the Coulomb interaction can be treated as a perturbation. The thus obtained electronic structure agrees with luminescence data. Additionally AlAs barriers are considered.

1,056 citations


BookDOI
01 Sep 1995
TL;DR: In this article, the authors describe the application of Ab Initio Electronic Structure Calculations to Molecules Containing Transition Metal Atoms (C W Bauschlicher Jr et al).
Abstract: Volume 2: Gaussian Basis Sets and Molecular Integrals (T Helgaker & P Taylor) Time Dependent Response Theory with Applications to Self Consistent Field and Multiconfiguration Self Consistent Field Wave Functions (J. Olsen & P Jorgensen) Evaluation of Bond Energies to Chemical Accuracy by Quantum Chemical Techniques (K Raghavachari & L A Curtiss) Exchange-Correlation Approximations in Density-Functional Theory (A D Becke) Coupled Cluster Theory - An Overview of Recent Developments (P J Bartlett) Pseudospectral Methods Applied to the Electron Correlation Problem (T J Martinez & E A Carter) Quasidegenerate Perturbation Theory Using Effective Hamiltonians (M Hoffmann) Analytical Derivative Techniques and the Calculation of Vibrational Spectra (P Pulay) Applications of Molecular Structure Methods to Problems in Astrochemistry (K P Kirby) The Application of Ab Initio Electronic Structure Calculations to Molecules Containing Transition Metal Atoms (C W Bauschlicher Jr et al) Studies of Electron Molecule Collisions on Massively Parallel Computers (C Winstead & V McKoy).

947 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present the implementation of the "conductor-like screening model" (COSMO) into the density functional program DMol, where the electronic structure and geometry of the solute are described by a density functional method (DFT).
Abstract: In this paper, we present the implementation of the ‘‘conductorlike screening model’’ (COSMO) into the density functional program DMol. The electronic structure and geometry of the solute are described by a density functional method (DFT). The solute is placed into a cavity which has the shape of the solute molecule. Outside of the cavity, the solvent is represented by a homogeneous dielectric medium. The electrostatic interaction between solute and solvent is modeled through cavity surface charges induced by the solvent. The COSMO theory, based on the screening in conductors, allows for the direct determination of the surface charges within the SCF procedure using only the electrostatic potentials. This represents the major computational advantage over many of other reaction field methods. Since the DMol/COSMO energy is fully variational, accurate gradients with respect to the solute coordinates can be calculated for the first time, without any restriction on the shape of the cavity. The solvation energies and optimized molecular structures are calculated for several polar solutes. In addition, the trends in basicity of amines and the relative stabilities of molecular conformers are studied. Our results suggest that for neutral solutes, agreement between calculated and experimental solvation energies of better than about 2 kcal/mol can be achieved.

743 citations


BookDOI
01 Jan 1995
TL;DR: In this article, a simple example of a simple exact cancelation scheme is given for the node problem in a quantum Monte Carlo setting. But the exact cancellation scheme does not consider the potential energy surface of the node.
Abstract: Overview of Quantum Monte Carlo. Node Structure. Solutions to the Node Problem. Exact Cancellation Schemes: General. Exact Cancellation: a Simple Example. Exact Cancellation: Stability. Exact Cancellation: Computational Details. The Molecular Ion H3+. The Molecule H2. Potential Energy Surface for the Reaction H + H2 -> H2 + H. The Helium Dimer He2. The H-He Interaction. Prognostication.

699 citations


Journal ArticleDOI
TL;DR: It is shown that the equivalent of the interlayer state in the case of the isolated boron nitride sheet plays the same role as in the bulk case in determing the band gap.
Abstract: The quasiparticle band structure of bulk hexagonal boron nitride is studied within the GW approximation for the self-energy operator. The influence of the interlayer distance on the band structure is investigated both within the local density approximation and the quasiparticle approach, and the importance of an interlayer state in determining the gap is demonstrated. Also, the quasiparticle band structure for an isolated sheet of boron nitride is calculated. We show that the equivalent of the interlayer state in the case of the isolated boron nitride sheet plays the same role as in the bulk case in determing the band gap.

528 citations


Journal ArticleDOI
TL;DR: In this paper, the electronic structures of the cubic layered d1 metals LaI2 and CeI2 were calculated using local density functional theory and the linear muffin-tin orbital method.
Abstract: The electronic structures of the cubic layeredd1 metals LaI2 and CeI2 were calculated using local density-functional theory and the linear muffin-tin orbital method. Special care was taken in the sphere packing used for the atomic spheres approximation. the band structure and the bonding were analysed in terms of projections of the bands onto orthogonal orbitals. The conduction-band structure could be calculated with a down-folded two-orbital basis which then served for the construction of an analytical 2×2 orthogonal, two-center tight-binding Hamiltonian. The conduction band has almost pure Ln-Ln 5d egcharacter. Thex2−y2contribution dominates and is two-dimensional and short ranged. Strong hybridization with the 3z2−1 orbital occurs near the saddle point, which is thereby lowered in energy and bifurcated due to thekz-dispersion provided by the 3z2−1 orbital. This strengthens the metal-metal bonds and prevents the nesting instability of the Fermi surface of the half filledx2−y2band. Within the limited accuracy of the LDA, the band structure of CeI2 was found to be identical to that of LaI2. The conduction-band 4f hybridizationVdf2(0) was analysed and found to be several times smaller than in fcc γ-Ce, in qualitative agreement with recent photoemission results [1]. Of importance for this reduction seems to be that the conduction band is formed by essentially only one orbital,\(Ce 5d_{x^2 - y^2 } \),that the number of Ce nearest-neighbors is small, and that the Ce−Ce distance is relatively large.

405 citations


Journal ArticleDOI
TL;DR: A simple model for the negative-$U$ behavior of hydrogen should be valid for H in any semiconductor, which is based on first-principles total-energy calculations.
Abstract: We have studied electronic structure, energetics, and migration of hydrogen and hydrogen complexes in GaN, based on first-principles total-energy calculations. Our calculations reveal a number of features very different from those exhibited by hydrogen in more traditional semiconductors such as Si or GaAs: a very large negative-$U$ effect ($U\ensuremath{\approx}2.4$ eV), the instability of the bond-center site, high energies for hydrogen molecules, and an unusual geometry for the Mg-H complex. All of these features are shown to be a consequence of distinctive properties of GaN, namely, the strongly ionic nature and the large bond strength of the Ga-N bond. We propose a simple model for the negative-$U$ behavior, which should be valid for H in any semiconductor.

383 citations


Journal ArticleDOI
TL;DR: In this article, the authors discuss the possibility of realizing half-metallic antiferromagnets, i.e., systems with 100% spin polarization of the conduction electrons without showing a net magnetization.
Abstract: This Letter discusses the possibility of realizing half-metallic antiferromagnets, i.e., systems with 100% spin polarization of the conduction electrons without showing a net magnetization. The predictions are based on electronic structure calculations using the local density approximation.

335 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical electronic structure based approach suitable for the study of complex silicas, and apply it to three different silica polymorphs, was developed. But the method is first principles but simplified to cope with large systems.
Abstract: We develop a theoretical electronic structure based approach suitable for the study of complex silicas, and apply it to three different silica polymorphs. The method is first principles but simplified to cope with large systems. Charge transfer between ions is included in a self-consistent fashion. The method is found to be adequate to describe the relative energies and the electronic structure of silica and is used to construct a simplified model energy for the structural transition of high cristobalite. In addition we have studied the moderately complex silica, melanophlogite. Melanophlogite, although a clathrate structure belonging to the group of silica polymorphs known as clathrasils, is found to be only 10 kJ/mol above \ensuremath{\alpha}-quartz, in accord with the recent thermochemical study of the stability of zeolites.

292 citations


Journal ArticleDOI
TL;DR: A third-neighbor tight-binding model, with spin-orbit coupling included, is developed, to treat the electronic properties of Bi and Sb quantitatively and should be useful for calculations of the electronic property of proposed semimetal-semiconductor systems, including superlattices and resonant-tunneling devices.
Abstract: We have developed a third-neighbor tight-binding model, with spin-orbit coupling included, to treat the electronic properties of Bi and Sb. This model successfully reproduces the features near the Fermi surface that will be most important in semimetal-semiconductor device structures, including (a) the small overlap of valence and conduction bands, (b) the electron and hole effective masses, and (c) the shapes of the electron and hole Fermi surfaces. The present tight-binding model treats these semimetallic properties quantitatively, and it should, therefore, be useful for calculations of the electronic properties of proposed semimetal-semiconductor systems, including superlattices and resonant-tunneling devices.

289 citations


Journal ArticleDOI
TL;DR: In this article, a generalization of classical adiabatic molecular dynamics, termed molecular dynamics with electronic frictions, is described for nuclear motion on a continuum of potential energy surfaces, such as for adsorbate dynamics at a metal surface.
Abstract: A generalization of classical adiabatic molecular dynamics, which we term molecular dynamics with electronic frictions, is described for nuclear motion on a continuum of potential‐energy surfaces, such as for adsorbate dynamics at a metal surface. In this situation, the Born–Oppenheimer approximation fails, since for any molecular motion—such as vibrations, rotations, or translations—there are resonant electronic excitations of the metal. However, such excitations are often highly delocalized, so that the continuum of electronic potential‐energy surfaces on which nuclear motion occurs are all of similar shape, and can be replaced by a single, effective potential. Nonadiabatic energy exchange between nuclear and electronic degrees of freedom is then represented by frictional and fluctuating forces on the nuclei, and no explicit electronic dynamics are required. The friction in general involves memory, although it is shown that the Markov limit in which memory vanishes is likely to be quite broadly applicab...

Journal ArticleDOI
TL;DR: A new approach to the calculation of the electronic structure of large systems within the local density approximation is outlined and ideal order-{ital N} scaling is obtained.
Abstract: A new approach to the calculation of the electronic structure of large systems within the local density approximation is outlined. The electronic structure problem is formulated using real space multiple scattering theory. Employing a compute-node $\ensuremath{\leftrightarrow}$ atom equivalence, the method has been implemented on a massively parallel processing supercomputer. The method is naturally highly parallel and ideal order- $N$ scaling is obtained. The convergence of the method is demonstrated by comparison with the result of conventional electronic structure calculation for elemental metals and through calculation of the ordering energy of $\ensuremath{\beta}$ brass.

Journal ArticleDOI
TL;DR: A method for performing electronic-structure calculations of the total energy and interatomic forces which scales linearly with system size is described and a spatially truncated Wannier-like representation for the electronic states is obtained.
Abstract: We describe a method for performing electronic-structure calculations of the total energy and interatomic forces which scales linearly with system size. An energy functional is introduced which possesses a global minimum for which (1) electronic wave functions are orthonormal and (2) the correct electronic ground-state energy is obtained. Linear scaling is then obtained by introducing a spatially truncated Wannier-like representation for the electronic states. The effects of this representation are studied in detail. Molecular-dynamics simulations using an orthogonal tight-binding basis and ab initio local-orbital density-functional methods are presented. We study both Car-Parrinello and conjugate-gradient molecular-dynamics schemes and discuss practical methods for dynamical simulation. A detailed connection between our method and the density matrix approach of Daw [Phys. Rev. B 47, 10 895 (1993)] and Li, Nunes, and Vanderbilt, [Phys. Rev. B 47, 10 891 (1993)] is also provided.


Journal ArticleDOI
TL;DR: In this article, the density of a molecule expanded in plane waves is decoupled from its periodic images using a fit to atom-centered Gaussians, which reproduces the long-range electrostatic potential of the original density.
Abstract: The density of a molecule expanded in plane waves is decoupled from its periodic images using a fit to atom‐centered Gaussians, which reproduces the long‐range electrostatic potential of the original density. The interaction energy between the cluster and its periodic images is calculated by an Ewald summation. The method has been applied to self‐consistent ab initio molecular dynamics calculations of charged and polar molecules. An atomic point charge model of the charge density is obtained, which can be used for classical molecular dynamics models and to couple classical and quantum mechanical simulations.

Journal ArticleDOI
TL;DR: In this article, the authors review the results to date for few-particle quantum dots (N < 10) and discuss the extent to which theoretical predictions emerging from detailed numerical calculations can be reproduced using analytically solvable microscopic models.
Abstract: Quantum dots are examples of nanostructures which are attracting much interest in the fields of both pure and applied physics. The smallest dots currently being fabricated contain N<10 interacting electrons and have an effective dimensionality d

Journal ArticleDOI
TL;DR: Significant differences between the mean-field methods in determining the minimum energy structure of a set of C{sub 10} and C{ sub 20} isomers are demonstrated and the crucial importance of an accurate account of electron correlation is demonstrated.
Abstract: The electronic structure of medium-size molecular carbon is determined by a variety of methods, including density functional, quantum chemistry, and quantum Monte Carlo approaches. We demonstrate (i) significant differences between the mean-field methods in determining the minimum energy structure of a set of C{sub 10} and C{sub 20} isomers, and (ii) the crucial importance of an accurate account of electron correlation which enables us to predict, e.g., that of the available geometries for C{sub 20} the relaxed graphite fragment (bowl) is lower in energy than either the ring or fullerene isomers. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.


Journal ArticleDOI
TL;DR: In this article, the relative energies of two hydroxymethyl conformers for each of the two chair forms (4C1 and 1C4) of β-d -glucose were calculated at much more complete levels of quantum mechanical (QM) electronic structure theory than previously, and relative free energies in solution were calculated by adding vibrational, rotational, and solvent effects.

Journal ArticleDOI
TL;DR: A detailed electronic structure description of the reduced blue copper active site has now been developed as mentioned in this paper, which is a key determining factor in the high reduction potentials generally observed for blue copper proteins.
Abstract: A detailed electronic structure description of the reduced blue copper active site has now been developed. Photoelectron spectroscopy (PES) of imidazole, dimethyl sulfide, and methanethiolate bound to Cu(I) sites at single crystal surfaces has been used to define normal Cu(I) bonding to ligands relevant to the blue copper site. Variable photon energy PES has been used to assign valence band spectra, assess metal-ligand covalency, and probe specific orbital contributions to Cu(I) bonding. Self Consistent Field-X{alpha}-Scattered Wave (SCF-X{alpha}-SW) molecular orbital calculations calibrated to the photoelectron spectra have been performed to quantitatively complement the experimental bonding descriptions. These calculations have been extended to the reduced blue copper active site in plastocyanin, the prototypical blue copper protein, to detail the electronic structure changes that occur relative to normal Cu(I) bonding and upon oxidation. Ionization energies have been used to estimate the electronic structure contributions to the reduction potential. The long Cu-thioether axial bond present at the active site destabilizes the oxidized state and is therefore a key determining factor in the high reduction potentials generally observed for blue copper proteins. Linear coupling terms have been evaluated for the distortions of a blue copper site unconstrained by the protein backbone. 99 refs., 22 figs.,more » 12 tabs.« less

Journal ArticleDOI
TL;DR: In this article, a linear combination of atomic orbital-molecular orbital approach within the density functional formalism was used to study the electronic structure, geometries, and magnetic moments of small Nin (n = 2−6, 8, 13) clusters.

Book
01 Jan 1995
TL;DR: 1.1.
Abstract: 1. Purification 2. Electronic Structure 3. Sequences of Polymers 4. Crystallographic Molecular Models 5. Noncovalent Forces 6. Atomic Details 7. Evolution 8. Counting Polypeptides 9. Symmetry 10. Chemical Probes of Structure 11. Immunochemical Probes of Structure 12. Physical Measurements of Structure 13. Folding and Assembly 14. Membranes

Journal ArticleDOI
01 May 1995-Nature
TL;DR: In this paper, the quantum ground state is dominated on average by configurations in which an H2 moiety is attached to a CH3 group forming a three-centre two-electron bond.
Abstract: HYPERCOORDINATE carbonium ions can be formed by protonating saturated hydrocarbons with superacids1–3. As this leaves a deficiency of bonding electrons, the resulting non-classical carbocations contain bonds in which two electrons are shared between three nuclei. Protonated methane, CH+5, might be seen as the prototype of such species1–3. But recent calculations4,5 have suggested that all five C–H bonds are effectively equivalent and exchange dynamically very rapidly. It was therefore concluded4 that CH+5 is a highly fluxional molecule without a definite structure, in which the representation in terms of three-centre two-electron bonding is misleading. Here we use a recently developed technique6 to perform ab initio electronic structure calculations that include quantum effects of the nuclei. We find that, although there are prominent quantum-mechanical effects on the structure, including fluxional-ity, pseudo-rotations and hydrogen scrambling, the quantum ground state is nevertheless dominated on average by configurations in which an H2 moiety is attached to a CH3 group forming a three-centre two-electron bond. To this extent, CH+5 should therefore resemble other carbonium ions.

Journal ArticleDOI
TL;DR: In this paper, a method for calculating the self-energy in the GW approximation that can be applied to systems containing $3d$ and $4f$ electrons is presented.
Abstract: We present a method for calculating the self-energy in the $\mathrm{GW}$ approximation that can be applied to systems containing $3d$ and $4f$ electrons. The method is applied to NiO and a gap of $\ensuremath{\sim}5.5$ eV is obtained, which is in reasonable agreement with the experimental value of 4.0 eV. The local density O $p$ band is also improved. The high binding energy satellite at 8 eV, however, is not obtained and there is no substantial increase of O $p$ character at the top of he valence band compared to the local density result. Based on our results, we discuss to which extent the $\mathrm{GW}$ approximation is capable of describing highly correlated systems such as NiO.

Journal ArticleDOI
TL;DR: Capacitance spectroscopy is used to determine the allowed energy levels for electrons and holes in InAs self-assembled quantum dots embedded in GaAs as discussed by the authors, which allows the construction of an energy level diagram for these quantum dots which correlates well with previously observed photoluminescence data.
Abstract: Capacitance spectroscopy is used to determine the allowed energy levels for electrons and holes in InAs self‐assembled quantum dots embedded in GaAs. Using this technique, the relative energy of the electron and hole states is measured with respect to their respective energy band minima in the GaAs. This allows the construction of an energy level diagram for these quantum dots which correlates well with previously observed photoluminescence data. By tuning the device geometry, a fine structure in the electron ground state is revealed and attributed to Coulomb charging effects.

Journal ArticleDOI
TL;DR: In this paper, an optical study of trivalent 3-d transition metal oxide compounds R M O 3 with perovskite-type structure has revealed the variation of their electronic structures with the 3-D element M and rare earth element R.
Abstract: Optical study of trivalent 3 d transition metal oxide compounds R M O 3 with perovskite-type structure has revealed the variation of their electronic structures with the 3 d element M and rare earth element R . The low energy feature is governed by electronic states in the M - O network. The charge gap, either of the Mott type or charge-transfer type, is observed for a series of R M O 3 compounds, except for metallic LaNiO 3 and LaCuO 3 compounds. The charge gap systematics has been accounted for in terms of a simple ionic model. However, the deviation from the ionic model is magnified in narrow gap compounds, where the M 3 d - O 2 p mixing appears to reshuffle the electronic states. The variation of the covalent nature of the M - O network in the RMO 3 compounds is also discussed in terms of the shell-model analysis of the phonon spectra.

Journal ArticleDOI
TL;DR: This work inverts a set of self-consistently determined screened LDA potentials for a range of bulk crystal structures and unit cell volumes, thus determining spherically symmetric and structurally averaged atomic potentials (SLDA), and finds that the adjustment represents a reasonably small perturbation over the SLDA potential.
Abstract: Transferable screened atomic pseudopotentials were developed 30 years ago in the context of the empirical pseudopotential method (EPM) by adjusting the potential to reproduce observed bulk electronic energies. While extremely useful, such potentials were not constrained to reproduce wave functions and related quantities, nor was there a systematic way to assure transferability to different crystal structures and coordination numbers. Yet, there is a significant contemporary demand for accurate screened pseudopotentials in the context of electronic structure theory of nanostructures, where local-density-approximation (LDA) approaches are both too costly and insufficiently accurate, while effective-mass band approaches are inapplicable when the structures are too small. We can now improve upon the traditional EPM by a two-step process: {ital First}, we invert a set of self-consistently determined screened LDA potentials for a range of bulk crystal structures and unit cell volumes, thus determining spherically symmetric and structurally averaged atomic potentials (SLDA). These potentials reproduce the LDA band structure to better than 0.1 eV, over a range of crystal structures and cell volumes. {ital Second}, we adjust the SLDA to reproduce {ital observed} excitation energies. We find that the adjustment represents a reasonably small perturbation over the SLDA potential, so that the ensuing fitted potentialmore » still reproduces a {gt}99.9% overlap with the original LDA pseudowave functions despite the excitation energies being distinctly non-LDA. We apply the method to Si and CdSe in a range of crystal structures, finding excellent agreement with the {ital experimentally} {ital determined} band energies, optical spectra {epsilon}{sub 2}({ital E}), static dielectric constants, deformation potentials, and, at the same time, {ital LDA{minus}quality} wave functions.« less

Journal ArticleDOI
TL;DR: An efficient approach is reported for performing self-consistent ab initio calculations of structural and electronic properties of II-VI semiconductors which overcomes to a large extent well-known shortcomings of the local-density approximation (LDA) for these d-band compounds.
Abstract: We report results of an efficient approach for performing self-consistent ab initio calculations of structural and electronic properties of II-VI semiconductors which overcomes to a large extent well-known shortcomings of the local-density approximation (LDA) for these d-band compounds. Dominant atomic self-interaction corrections are taken into account by employing appropriately constructed pseudopotentials in the framework of standard LDA calculations. Our results for ZnO, ZnS, CdS, and CdSe are in excellent agreement with a whole body of experimental data.

Journal ArticleDOI
Kazuto Akagi1, Ryo Tamura1, Masaru Tsukada1, Satoshi Itoh2, Sigeo Ihara2 
TL;DR: General features of the electronic states of helically coiled cages of graphite layer, which are studied by simple tight-binding models, show semimetallic character having a sharp peak at the Fermi level, which might cause interesting properties such as the superconducting ones.
Abstract: General features of the electronic states of helically coiled cages of graphite layer are studied by simple tight-binding models. The topological structure of the cages, which is determined by the distributions of the 5-membered and 7-membered rings, governs the electronic behavior around the Fermi level. Unlike the carbon nanotubes, some types of them show semimetallic character having a sharp peak at the Fermi level, which might cause interesting properties such as the superconducting ones.

Journal ArticleDOI
Robert Tycko1, S. E. Barrett1, Gary Dabbagh1, L. N. Pfeiffer1, K. W. West1 
09 Jun 1995-Science
TL;DR: Radio-frequency measurements reveal effects of electron-electron interactions on the energy levels and spin states of the two-dimensional electron system confined in the GaAs wells and rapid, temperature-independent relaxation at intermediate v values indicates a manifold of low-lying electronic states with mixed spin polarizations.
Abstract: An optical pumping technique was used to enhance and localize nuclear magnetic resonance (NMR) signals from an n-doped GaAs/Al0.1Ga0.9As multiple quantum well structure, permitting direct radio-frequency measurements of gallium-71 NMR spectra and nuclear spin-lattice relaxation rates (1/T1) as functions of temperature (1.6 K < T < 4.2 K) and the Landau level filling factor (0.66 < v < 1.76). The measurements reveal effects of electron-electron interactions on the energy levels and spin states of the two-dimensional electron system confined in the GaAs wells. Minima in 1/T1 at v approximately 1 and v approximately 2/3 indicate energy gaps for electronic excitations in both integer and fractional quantum Hall states. Rapid, temperature-independent relaxation at intermediate v values indicates a manifold of low-lying electronic states with mixed spin polarizations.