Volume 126, Issue 9, 07 March 2007
Index of content:
126(2007); http://dx.doi.org/10.1063/1.2565690View Description Hide Description
Correlation effects within the GW approximation have been incorporated into the Keldysh nonequilibrium transport formalism. We show that GW describes the Kondo effect and the zero-temperature transport properties of the Anderson model fairly well. Combining the GW scheme with density functional theory and a Wannier function basis set, we illustrate the impact of correlations by computing the characteristics of a hydrogen molecule between two Pt chains. Our results indicate that self-consistency is fundamental for the calculated currents, but that it tends to wash out satellite structures in the spectral function.
126(2007); http://dx.doi.org/10.1063/1.2712839View Description Hide Description
The authors propose a new approach to vibration spectroscopy based on the coherent anti-Stokes Raman scattering of broadband ultrashort laser pulses. The proposed method reveals both the amplitude and the phase of molecular vibrations by utilizing the cross-correlation frequency resolved optical gating (XFROG) technique. The spectrum of the anti-Stokes pulse is measured as a function of the time delay between the laser-induced molecular vibrations and a well characterized broadband femtosecond probe pulse. The iterative XFROG algorithm provides a simultaneous complete characterization of molecular vibrations both in frequency and time domains with high resolution. They demonstrate experimentally the feasibility of the proposed method and show one of its potential applications in disentangling the time behavior of a mixture of vibrationally excited molecules. The technique of femtosecond pulse shaping is used for further improvement of accuracy and stability against noise.
Phase separation of acetonitrile-water mixtures and minimizing of ice crystallites from there in confinement of MCM-41126(2007); http://dx.doi.org/10.1063/1.2712432View Description Hide Description
The effect of confinement of an acetonitrile-water mixture, whose correlation length was comparable to the pore size of the mesopores of MCM-41 , on the phase changes was studied. Used techniques were low temperature differential scanning calorimetry and Fourier transform infrared spectroscopy, where the phase separation, lowering of the freezing and melting temperatures, and phase transitions of the acetonitrile were detected. The latter occurred in the mesopores at temperatures similar to that of the pure liquid, while the melting temperature of the water in the mesopores decreased markedly at higher acetonitrile contents, suggesting a marked lowering of ice crystallite size.
126(2007); http://dx.doi.org/10.1063/1.2711804View Description Hide Description
By measuring diffusion rate, the conformation change of single poly(2-vinylpyridine) chain in aqueous solution was studied by fluorescencecorrelation spectroscopy. The data showed a stepwise change of hydrodynamic radius when value was tuned, reflecting a sign of first-order conformation transition, and a continuous change was found at varying salt concentration.
126(2007); http://dx.doi.org/10.1063/1.2515315View Description Hide Description
Nonequilibrium molecular dynamics simulations of hen egg white lysozyme have been performed in the canonical ensemble at in the presence of external electromagnetic fields of varying intensity in the microwave to far-infrared frequency range. Significant nonthermal field effects were noted, such as marked changes in the protein’ssecondary structure which led to accelerated incipient local denaturation relative to zero-field conditions. This occurred primarily as a consequence of alignment of the protein’s total dipole moment with the external field, although the enhanced molecular mobility and dipolar alignment of water molecules is influential on sidechain motion in solvent-exposed regions. The applied field intensity was found to be highly influential on the extent of denaturation in the frequency range studied, and fields were found to induce initial denaturation to a comparable extent to thermal denaturation in the 400 to range. In subsequent zero-field simulations following exposure to the e/m field, the extent of perturbation from the native fold and the degree of residual dipolar alignment were found to be influential on incipient folding.