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This paper presents a theoretical approach to the evaluation of polaron binding energy in polymers. Quantum chemical calculations were performed on a model polymer, poly[methyl(phenyl)silylene], employing the B3LYP and CAM-B3LYP method. The polaron binding energy consists of two terms: the molecular deformation energy and electron-phonon term. Its value was found to be about 0.23 eV at the CAM-B3LYP/6-31G level of theory.
Dielectric properties of Eu(0.5)Ba(0.5)TiO(3) ceramics were investigated between 10 and 300 K in the frequency range of 1 MHz-100 THz. Permittivity exhibits a strong peak near the ferroelectric phase transition at 215 K. This is mainly due to softening of the lowest frequency polar phonon revealed in THz and infrared spectra. Dielectric relaxation was observed also below the ferroelectric soft mode frequency in the whole investigated temperature region, but it is probably caused by some defects such as Eu(3 + ) cations or oxygen vacancies. This implies that the ferroelectric phase transition has predominantly a displacive character. Raman scattering spectra revealed a lowering of crystal symmetry in the ferroelectric phase and XRD analysis indicated orthorhombic A2mm symmetry below 215 K. The magnetic measurements performed at various frequencies in the field cooled and field heating regime after cooling in zero magnetic fields excluded spin glass behavior and proved an antiferromagnetic order below 1.9 K in Eu(0.5)Ba(0.5)TiO(3).
An increased circular dichroism (CD) signal of large molecular aggregates formed upon DNA condensation was observed a long time ago, and is often referred to as psi-CD. The effort to understand this phenomenon is further motivated by the latest DNA packing studies and advances in macromolecular chemistry. In the present work, the transition dipole coupling model describing interactions of molecules with light has been extended to handle systems of arbitrary size. The analytical formulae obtained retain the simplicity and computational speed of the standard approach. The origin of the psi-effect was investigated on several model systems. The results suggest that the CD enhancement is primarily caused by delocalized phonon-like excitations in nucleic acid strands. The size of the system exhibiting the effect thus does not need to be comparable with or greater than the wavelength of the absorbed light. Small structural irregularities still allow for the enhancement while a larger disorder breaks it. The modeling is consistent with previous experimental electronic and vibrational CD studies, and makes it possible to correlate the enhancement with the geometry of the nucleic acid systems. 2008 Wiley Periodicals, Inc.
