Search results for "Anisotropy"
showing 10 items of 912 documents
Interacting induced dipoles polarization model for molecular polarizabilities. Reference molecules, amino acids and model peptides
1999
Abstract We outline a method for the calculation of molecular dipole ( μ ) and quadrupole ( Θ = ) moments and dipole–dipole polarizabilities ( α = ) which we have successfully applied to a series of reference molecules, amino acids and model peptides. The results for μ are in line with CPHF reference calculations. In particular, the calculated positive value of CO is in agreement with both experimental and CI calculations. The computation of ( α = ) has been performed by the interacting induced dipoles polarization model that calculates tensor effective anisotropic point polarizabilities (method of Applequist et al.). The POLAR program cannot be used as a black box. Some tests should be per…
The effect of temperature on the internal dynamics of dansylated POPAM dendrimers
2011
The internal and rotational dynamics of the dansylated poly(propylene amine) dendrimers (POPAM) have been studied by time correlated single photon counting (TCSPC) and molecular dynamics (MD) simulations. The hydrodynamic volumes of the dendrimer generations from G1 to G4 were estimated by fluorescence anisotropy data. Experiments and simulations suggest that the volume and the shape of the dendrimers are temperature dependent. At low temperatures the dendrimer structure becomes more spacious and rigid and back-folding of the individual branches is slowed down. For the G3 and G4 generations the temperature effects are much stronger than for the smaller G1 and G2 generations, where back-fold…
Magnetic Excitations in Polyoxometalate Clusters Observed by Inelastic Neutron Scattering: Evidence for Anisotropic Ferromagnetic Exchange Interacti…
1999
The ground-state properties of the tetranuclear Co2+ cluster [Co4(H2O)2(PW9O34)2]10- were investigated by combining specific heat, magnetic susceptibility, and magnetization measurements with a detailed inelastic neutron scattering (INS) study on a fully deuterated sample of K10[Co4(H2O)2(PW9O34)2]·22H2O. As a result of the single ion anisotropy of the octahedral Co2+, the appropriate exchange Hamiltonian of the Co4 spin cluster is anisotropic. INS turns out to be essential for the determination of energy splittings in the ground state resulting from the coupling. Besides the energy pattern, INS provides information about the wave functions of the split ground-state components of the spin c…
Magnetic Excitations in Polyoxometalate Clusters Observed by Inelastic Neutron Scattering: Evidence for Ferromagnetic Exchange Interactions and Spin…
1999
The ground-state properties of the tetranuclear Ni2+ cluster [Ni4(H2O)2(PW9O34)2]10- were investigated by combining magnetic susceptibility and magnetization measurements with a detailed inelastic neutron scattering (INS) study on a fully deuterated sample of K6Na4[Ni4(H2O)2(PW9O34)2]·24H2O. The temperature dependence of the magnetic susceptibility indicates a ferromagnetic coupling of the four constituent Ni2+ ions (s = 1), and a low-temperature magnetization study provides the magnitude of the S = 4 ground-multiplet splitting due to the single-ion anisotropy of the Ni2+ ions. Besides a more direct and precise determination of the anisotropic S = 4 ground-multiplet splitting, INS enabled t…
Magnetic polyoxometalates: anisotropic exchange interactions in the moiety of [(NaOH2)Co3(H2O)(P2W15O56)2]17-.
2005
The magnetic exchange interactions in a C0(3)(11) moiety encapsulated in Na(17) [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)] (NaCo(3)) were studied by a combination of magnetic measurements (magnetic susceptibility and low-temperature magnetization), with a detailed Inelastic Neutron Scattering (INS) investigation. The novel structure of the salt was determined by X-ray crystallography. The ferromagnetic Co(3)O(14) triangular cluster core consists of three octahedrally oxo-coordinated Co(II) ions sharing edges. According to the single-ion anisotropy and spin-orbit coupling usually assumed for octahedral Co(II) ions, the appropiate exchange Hamiltonian to describe the ground-state properties o…
Magnetism in Polyoxometalates: Anisotropic Exchange Interactions in the Co Moiety of [Co3W(D2O)2(ZnW9O34)2]12−—A Magnetic and Inelastic Neutron Scatt…
2002
The ground-state properties of a Co moiety encapsulated in a polyoxometalate anion were investigated by combining measurements of specific heat, magnetic susceptibility, and low-temperature magnetization with a detailed inelastic neutron scattering (INS) study on a fully deuterated polycrystalline sample of Na12[Co3W(D2O)2(ZnW9O34)2]⋅40 D2O (Co3). The ferromagnetic Co3O14 cluster core consists of three octahedrally oxo-coordinated CoII ions. According to the single-ion anisotropy and spin–orbit coupling of the octahedral CoII ions, the appropriate exchange Hamiltonian to describe the ground-state properties of the Co3 spin cluster is anisotropic and is expressed as ℋ=−2Σ(JŜ1αŜ2α+JŜ2αŜ3α), w…
Computer simulations of electron paramagnetic resonance spectra of P2O5Li2WO4Li2O glasses
1992
Abstract P2O5Li2WO4Li2O glasses have been synthesized and studied over a wide range of compositions. The glasses were characterized mainly by thermodifferential analysis and electron paramagnetic resonance (EPR). The EPR spectra are characterized by the presence of two signals with very different intensities, associated with the Wv (major signal) and Mov (minor signal) paramagnetic centres. The signals have been satisfactorily reproduced by computer simulation, assuming anisotropy in the g values as well as the hyperfine parameters and linewidths. EPR parameters have been extracted and indicate metallic ions located in environments close to square pyramidal.
Fluctuations and elastic properties of lipid membranes in the gel Lβ′ state: a coarse-grained Monte Carlo study
2010
We study the stress distribution profiles and the height and thickness fluctuations of lipid membranes in the gel L-beta ' state by Monte Carlo simulations of a generic coarse-grained model for lipid membranes, which reproduces many known properties of dipalmitoylphosphatidyncholine (DPPC) bilayers. The results are related to the corresponding properties of fluid membranes, and to theoretical predictions for crystalline and hexatic membranes. One striking observation is that the spontaneous curvature of the monolayers changes sign from the fluid to the gel phase. In the gel-phase, the long-wavelength height fluctuations are suppressed, and the fluctuation spectrum is highly anisotropic. In …
Anisotropy of the refractive index and absorption coefficient in the layer plane of gallium telluride single crystals
1995
Refractive index and absorption coefficient of GaTe for light polarized in the optical axis directions in the layer plane are determined from transmission measurements. The refractive index is determined in the wavelength range from 0.7 to 25 μm and the absorption coefficient in the range of energies from 1.6 to 2 eV at room temperature and at 30 K. The optical constants are found to be anisotropic in the layer plane. The refractive index dispersion is interpreted through a Phillips-Van Vechten model and the Penn gaps for each direction are found to be E pg (⊥b) = 3.37 eV and E pg (∥b) = 3.58 eV. In the long-wavelength region a polar phonon contribution is also taken into account. The absor…
Magnetic field-induced alignment of molecular rotor-shaped cyclophanes
2010
Molecular pinwheels consisting of dipolar substituted cyclophanes in solution can function as free microscopic rotors in the presence of a homogeneous static magnetic field B and a circularly polarized electric field E rotating on a plane containing B. Owing to the high magnetic anisotropy of [26](1,2,3,4,5,6)cyclophane and [36](1,2,3,4,5,6)cyclophane biased by strong ring currents, ∼1 in 105 molecules are expected to align with the C6 symmetry axis perpendicular to a magnetic field of 21 T. The magnetic-field-controlled alignment of rotor-shaped cyclophanes is insignificantly affected by nonpolar solvents, for example, toluene.