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A polythiophene derivative bearing TEMPO radical was synthesized by oxidative chemical polymerization of its monomer. The polymer had a high spin density (2.05 × 10 21 spins/g of polymer). CV studies of the polymer showed that the electrochemical redox reaction of the TEMPO radicals were completely reversible. We demonstrated, for the first time, construction and charge/discharge characteristics of an organic radical battery utilizing a TEMPO bearing polythiophene based cathode material. The battery had an initial specific discharge capacity of 79 A h/kg (87% of the theoretical capacity) and an average output voltage of 3.6 V. The specific energy capacity initially discharged was 268 W h/kg.

First-principles calculations have been carried out to obtain the size- and shape-dependent energetics of the nanocrystals made of transition-metal elements Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au. A structural parameter characterizing the nanocrystal size and shape has been devised, which is a combination of variables such as the total and surface number of atoms. With the aid of the latter, structure–property relationships have been formulated, interlinking the (first-principles) energetics to (atomistic) structure.

A computational modeling methodology is described, which is based on the total-energy and defect calculations using the density and hybrid functionals in combination with the supercell approach. This methodology is employed to study the structure and energetics of zinc oxide (ZnO) nanowires, and the electrical properties of a bismuth-doped zinc oxide (ZnO:Bi) nanowire. A simple model is developed, where the nanowire formation energy is expressed as a function of the nanowire diameter and cross-sectional morphology (hexagonal or triangular). Defect calculations are employed to characterize the ZnO:Bi nanowire, in regard to the location and charge-state of the dopant. The latter indicates that the dopant atoms are mostly substituted into the Zn sites on the nanowire surface, and therefore Bi in ZnO electrically acts as a donor.

We performed ab initio zero temperature and finite temperature molecular dynamics calculations to investigate the homoepitaxial growth on the Si(0 0 1) surface. How do the deposited atoms (adatoms) form addimers and how do the addimers reach their favorable positions at the nucleation site of the growth process are presented. Once two epitaxial addimers, one over the dimer row and oriented perpendicular to the surface dimer bonds and the other over the adjacent trough, are aligned at high temperature, the nucleation site of the growth process is formed. The concerted bond exchange between these addimers and the reconstructed surface dimers is found to be the atomistic mechanism that leads to the homoepitaxial growth. © 2001 Elsevier Science B.V.

We predict new forms of carbon consisting of one and two dimensional networks of interlinked single wall carbon nanotubes, some of which are energetically more stable than van der Waals packing of the nanotubes on a hexagonal lattice. These interlinked nanotubes are further transformed with higher applied external pressures to more dense and complicated stable structures, in which curvature-induced carbon sp$^{3}$ re-hybridizations are formed. We also discuss the energetics of the bond formation between nanotubes and the electronic properties of these predicted novel structures., Comment: 4 pages, 4 postscript figures; To be appear in PRB

We present a first-principles study to elucidate the nature of the bonding, stability, energetics, and dynamics of individual X8H8 molecules (X = C, Si, Ge). The results obtained from both “local basis” and “pseudopotential” ab initio methods are in good agreement with the experimental data that exists for cubane (C8H8). The trends among these molecules are reminiscent of those prevailing in the bulk solids of C, Si, and Ge. High-temperature dynamics and fragmentation of X8H8 were studied by the quantum molecular dynamics method which shows that at high temperatures cubane is transformed to the 8-fold ring structure of cyclooctotetraene.

First-principles total-energy calculations for hydrogen impurities in CuInSe2 (CIS) and CuGaSe2 (CGS) show that H+ takes up the Cu–Se bond center position, whereas H0 and H− take up tetrahedral interstitial site next to In (in CIS) or Ga (in CGS). Hydrogen creates a negative-U center (i.e., H0 is never stable), with a (+/−) transition level at Ec−0.39 eV in CIS, and Ec−0.57 eV in CGS. However, once combined with the 2VCu−+IIICu2+ complex, hydrogen forms shallower centers with transition levels at Ec−0.15 eV in CIS, and Ec−0.39 eV in CGS. We conclude that hydrogen could convert CIS to n type, but not CGS.

First-principles total-energy calculations suggest that interstitial hydrogen impurity forms a shallow donor in SnO2, CdO, and ZnO, but a deep donor in MgO. We generalize this result to other oxides by recognizing that there exist a “hydrogen pinning level” at about 3.0±0.4 eV below vacuum. Materials such as Ag2O, HgO, CuO, PbO, PtO, IrO2, RuO2, PbO2, TiO2, WO3, Bi2O3, Cr2O3, Fe2O3, Sb2O3, Nb2O5, Ta2O5, FeTiO3, and PbTiO3, whose conduction band minimum (CBM) lie below this level (i.e., electron affinity>3.0±0.4 eV) will become conductive once hydrogen is incorporated into the lattice, without reducing the host. Conversely, materials such as BaO, NiO, SrO, HfO2, and Al2O3, whose CBM lie above this level (i.e., electron affinity

Electrodes made of organic polymers bearing redox-active radical pendant groups have attractive features for use in rechargeable batteries. Electronic structure and electrochemical properties of cathode-and anode-active organic polymers are investigated here by means of first-principles calculations performed in the framework of the density functional theory. We consider organic radical polymers (ORPs) that consist of trans-polyacetylene derivatives bearing a variety of nitroxide radicals. A number of neutral and charged supercells are utilized to compute the ionization potentials and electron affinities as well as the one-electron states of these ORPs. By revealing the polyacetylene-derived highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) as well as the radical-derived singly occupied molecular orbital (SOMO), the variation of the SOMO energy within the HOMO-LUMO gap is determined in the course of the oxidization or reduction of ORPs. Our results indicate that the ionization potential I and electron affinity A of polyacetylene would act as a lower or upper bound in the variation of the electrochemical potential of cathode- or anode-active ORPs in the course of battery discharge or charge owing to pinning of the radical-derived SOMO to the polyacetylene-derived HOMO or LUMO. Accordingly, it is anticipated that the electrochemical "window" [-I,-A] of the polymeric backbone of ORPs will impose certain limitations in accomplishing a high charge/discharge voltage range in a totally organic rechargeable battery with positive and negative electrodes made of cathode-and anode-active ORPs, respectively. On the other hand, our findings suggest that one could, in principle, take advantage of using two different (conducting) polymeric backbones in the anode and cathode with adjusted HOMO and LUMO offsets once the electron transfer is accomplished to take place through the conducting backbones.

An impurity in a semiconductor can have either amphoteric behavior (no net production of electron or holes), or be an energetically deep center (carriers produced only at high temperature), or a shallow center (carriers produced even at low temperature). In most semiconductors (e.g., Si, GaAs, GaP, InP, and ZnSe) hydrogen impurities do not produce free carriers, being instead an amphoretic center; yet hydrogen does dope n-type some oxides such as ${\mathrm{SnO}}_{2}$ and ZnO. We studied theoretically whether or not H could dope chalcopyrite ${\mathrm{I}\ensuremath{-}\mathrm{I}\mathrm{I}\mathrm{I}\ensuremath{-}\mathrm{V}\mathrm{I}}_{2}$ compounds, ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}.$ Based on the first-principles calculations, we find that nonsubstitutionally incorporated hydrogen forms a deep donor in ${\mathrm{CuGaSe}}_{2},$ but a relatively shallow donor in ${\mathrm{CuInSe}}_{2}.$ The interaction of hydrogen with the abundant defect complex ${(2V}_{\mathrm{Cu}}+{\mathrm{In}}_{\mathrm{Cu}}{)}^{0}$ yields an even shallower donor, making ${\mathrm{CuInSe}}_{2}$ n type. In addition, our results show that hydrogen passivates the acceptorlike copper vacancies in both ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2},$ thus eliminating p type behavior. These findings, in conjunction with typical conditions under which ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}$ are grown, indicate that ${\mathrm{CuInSe}}_{2}$ could be doped n type via hydrogen incorporation, whereas ${\mathrm{CuGaSe}}_{2}$ could not. The reason for the different behavior of ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}$ towards hydrogen is that in the latter case the conduction-band minimum is at a considerably higher energy than in the former case. Despite this difference in electrical properties, it is predicted that hydrogen can be stored in both ${\mathrm{CuInSe}}_{2}$ and ${\mathrm{CuGaSe}}_{2}$ via implantation since the implanted hydrogens decorate copper atoms as well as preexisting copper vacancies.

SnO2 is a prototype "transparent conductor," exhibiting the contradictory properties of high metallic conductivity due to massive structural nonstoichiometry with nearly complete, insulator-like transparency in the visible range. We found, via first-principles calculations, that the tin interstitial and oxygen vacancy have surprisingly low formation energies and strong mutual attraction, explaining the natural nonstoichiometry of this system. The stability of these intrinsic defects is traced back to the multivalence of tin. These defects donate electrons to the conduction band without increasing optical interband absorption, explaining coexistence of conductivity with transparency.

The electronic and structural properties of molecular and solid cubane have been studied by first-principles, self-consistent field total energy calculations. Calculated molecular properties such as equilibrium geometry and electronic and vibrational spectra are found to be in good agreement with experimental data. Structural parameters and the energetics of both the low-temperature, orientationally ordered and high-temperature, orientationally disordered or plastic phases of solid cubane are determined. The valence band of solid cubane is derived from the molecular states; the energy gap between the lowest unoccupied and highest occupied molecular orbital bands is rather large due to the saturated carbon atoms. The effect of alkali-metal-atom doping on the electronic energy bands is investigated. It is found that the metallic band of doped cubane is derived from the undoped solid cubane's lowest conduction band with a significant contribution from the alkali-metal atom.

Cubane (C8H8) is an immensely strained molecule whose C-C-C bond angle is 90 degrees rather than 109.5 degrees as expected for sp(3) bonding of carbon. We have measured the intramolecular vibrational spectrum of cubane using inelastic neutron scattering. The neutron data are used to test the transferability of various phenomenological potentials and tight-binding models to this highly strained molecule. Unlike these models, first-principles calculations of the INS spectrum (both energy and intensity) agree well with the experimental data.