H.E. Roman

Folding and aggregation of designed proteins

Protein aggregation is studied by following the simultaneous folding of two designed identical 20-letter amino acid chains within the framework of a lattice model and using Monte Carlo simulations. It is found that protein aggregation is determined by elementary structures (partially folded intermediates) controlled by local contacts among some of the most strongly interacting amino acids and formed at an early stage in the folding process.

ELECTRON-PHONON COUPLING IN CHARGED BUCKMINSTERFULLERENE

Abstract A simple, yet accurate solution of the electron–phonon coupling problem in C60 is presented. The basic idea behind it is to be found in the parametrization of the ground state electronic density of the system calculated making use of ab initio methods, in term of sp2+x hybridized orbitals. This parametrization allows for an economic determination of the deformation potential associated with the fullerenes normal modes. The resulting electron–phonon coupling constants are used to calculate Jahn–Teller effects in C60−, and multiple satellite peaks in the corresponding photoemission reaction. Theory provides an accurate account of the experimental findings.

The valence of small fullerenes

Abstract The production and isolation of small fullerenes and of their stable compounds and the knowledge of their chemistry should pave the way to the syntesis of novel carbon-based cluster-assembled materials like carbon clathrates, hollow diamonds and diamond-like thin films. In this quest, the knowledge of the valence of the small fullerenes is essential. We report here that the small fullerenes C n (20 ≤ n ≤ 32), aside from the well known values associated with the local one electron picture of dangling bonds, display hidden valences connected with the free electron picture of the shell structure of π-electrons.

High-current field emission from an atomic quantum wire

Abstract The electromagnetic response of linear carbon chains to external fields have been studied, making use of ab-initio methods. It is found that the associated emission currents, plotted as a function of the bias potential, follow Fowler-Nordheim intensity-voltage curves typical of the field emission of metallic tips. Under standard bias conditions, linear carbon chains of one nanometer of length are expected to deliver currents of the order of one microampere. These systems behave, furthermore, as conducting spheroidal particles in photoabsorption processes. Linear carbon chains are thus likely to constitute the ultimate atomic-scale realization of metallic wires.

Long wavelength optical response of incipient fullerene nanotubes

Abstract The electromagnetic response of elongated fullerenes is calculated in the time-dependent local density approximation. The long wavelength optical behaviour of these systems is found to be very similar to that expected for the case of elongated metallic particles.

Electromagnetic response of quasispheroidal fullerene C70

Abstract The optical/UV spectra of C 70 provide direct evidence for the coupling of electronic motion to distortions of the fullerence surface. The difference between the spectrum obtained when the electric field of the photon is parallel to the long axis of the molecule and when it is perpendicular to it, appears to depend sensitively on the effective quadrupole distortion of the fullerenes mean field.

Electron-phonon interaction in C70

The matrix elements of the deformation potential of C

Electron-phonon interaction in C 70

_{70}

Field emission properties of linear carbon clusters

are calculated by means of a simple, yet accurate solution of the electron-phonon coupling problem in fullerenes, based on a parametrization of the ground state electronic density of the system in terms of

Evolution of the plasmon spectrum of C28Hn with the passivation of dangling bonds

sp^{2+x}