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Angular Distribution Functions (angular + distribution_function)
Selected AbstractsTheoretical Study on Co3+ in Aqueous Solution in Terms of ABEEM/MM ModelCHINESE JOURNAL OF CHEMISTRY, Issue 6 2007Qing-Mei Guan Abstract A detailed theoretical investigation on Co3+ hydration in aqueous solution has been carried out by means of molecular dynamics (MD) simulations based on the atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM). The effective Co3+ ion-water potential has been constructed by fitting to ab initio structures and binding energies for ionic clusters. And then the ion-water interaction potential was applied in combination with the ABEEM-7P water model to molecular dynamics simulations of single Co3+(aq.) solution, managing to reproduce many experimental structural and dynamical properties of the solution. Here, not only the common properties (radial distribution function, angular distribution function and solvation energy) obtained for Co3+ in ABEEM-7P water solution were in good agreement with those from the experimental methods and other molecular dynamics simulations but also very interesting properties of charge distributions, geometries of water molecules, hydrogen bond, diffusion coefficients, vibrational spectra are investigated by ABEEM/MM model. [source] An Ab Initio Molecular Dynamics Study of Bioactive Phosphate Glasses,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Emilia Tang First principles molecular dynamics simulations of ternary phosphate-based glasses P2O5CaONa2O (PBGs) have been carried out in order to provide an accurate description of the local structure and properties of these important materials for biomedical applications. The structures of PBGs with compositions (P2O5)0.45(CaO)x(Na2O)0.55,,,x (x,=,0.30, 0.35, and 0.40) were generated using a full ab initio molecular dynamics melt-and-quench procedure. The analysis of the structure of the glasses at 300,K shows the prevalence of the metaphosphate Q2 and pyrophosphate Q1 species, whereas the number of Q3 units, which constitute the three-dimensional phosphate network, significantly decreases with the increase in calcium content in the glass. Calculation of the pair and angular distribution functions suggests that the rigidity of the phosphate tetrahedral glass network increases with the concentration of calcium, an observation which is interpreted in terms of the tendency of Ca2+ to be a stronger coordinator than sodium. [source] Tl(I)-the strongest structure-breaking metal ion in water?JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2007A quantum mechanical/molecular mechanical simulation study Abstract Structural and dynamical properties of the Tl(I) ion in dilute aqueous solution have been investigated by ab initio quantum mechanics in combination with molecular mechanics. The first shell plus a part of the second shell were treated by quantum mechanics at Hartree-Fock level, the rest of the system was described by an ab initio constructed potential. The radial distribution functions indicate two different bond lengths (2.79 and 3.16 Å) in the first hydration shell, in good agreement with large-angle X-ray scattering and extended X-ray absorption fine structure spectroscopy results. The average first shell coordination number was found as 5.9, and several other structural parameters such as coordination number distributions, angular distribution functions, and tilt- and ,-angle distributions were evaluated. The ion,ligand vibration spectrum and reorientational times were obtained via velocity auto correlation functions. The TlO stretching force constant is very weak with 5.0 N m,1. During the simulation, numerous water exchange processes took place between first and second hydration shell and between second shell and bulk. The mean ligand residence times for the first and second shell were determined as 1.3 and 1.5 ps, respectively, indicating Tl(I) to be a typical "structure-breaker". The calculated hydration energy of ,84 ± 16 kcal mol,1 agrees well with the experimental value of ,81 kcal mol,1. All data obtained for structure and dynamics of hydrated Tl(I) characterize this ion as a very special case among all monovalent metal ions, being the most potent "structure-breaker", but at the same time forming a distinct second hydration shell and thus having a far-reaching influence on the solvent structure. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Probability distribution functions for the Sun's magnetic fieldASTRONOMISCHE NACHRICHTEN, Issue 6 2010J.O. Stenflo Abstract Magnetoconvection structures the Sun's magnetic field cover a vast range of scales, down to the magnetic diffusion scale that is orders of magnitude smaller than the resolution of current telescopes. The statistical properties of this structuring are governed by probability density functions (PDFs) for the flux densities and by the angular distribution functions for the orientations of the field vectors. The magnetic structuring on sub-pixel scales greatly affects the field properties averaged over the resolution element due to the non-linear relation between polarization and magnetic field. Here we use a Hinode SOT/SP data set for the quiet Sun disk center to explore the complex behavior of the 6301,6302 Å Stokes line profile system and identify the observables that allow us to determine the distribution functions in the most robust and least model dependent way. The angular distribution is found to be strongly peaked around the vertical direction for large flux densities but widens with decreasing flux density to become isotropic in the limit of zero flux density. The noise-corrected PDFs for the vertical, horizontal, and total flux densities all have a narrowly peaked maximum at zero flux density that can be fitted with a stretched exponential, while the extended wings decline quadratically (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||