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The structure of rarefied and densified PbSiO3 glass: a molecular dynamics study

Bergmański G., Białoskórski M., Rychcik-Leyk M., Witkowska A., Rybicki J., Mancini G., Frigio S., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2004

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Vol. 8, No 3

393-412

EN

The paper is a molecular dynamics (MD) study of the structure of rarefied and densified lead-silicate glass of the PbSiO3 composition. Simulations have been performed in the constant volume regime for systems with densities of 3000, 4000, 5000, 5970 (normal density), 7000 and 8000kg/m3, using a two-body potential (Born-Mayer repulsive forces and Coulomb forces due to full ionic charges). All the systems were initially prepared as well equilibrated hot melts, and then slowly cooled down to 300K. The information on short-range correlations was obtained in a conventional way (from radial and angular distribution functions), while the middle-range order was studied via cation-anion ring analysis, using our new programme for basal ring determination. The structure of rarefied and densified glasses is compared with the structure of the same glasses under normal conditions. Moreover, the present results on PbSiO3 glass are compared with the corresponding data previously obtained for rarefied and densified PbGeO3 glass (Rybicki et al. 2001 Comput. Met. Sci. Technol. 7 91-112).

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A comparison between MD- and EXAFS-extracted structural data for ternary RbBrl – xIx

Bosko J., Rybicki J., Witkowska A., Principi E.

Computational Methods in Science and Technology

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2002

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Vol. 8, nr 2

7--12

EN

The structure of ternary salts of the composition RbBr1-xIx, x = 0.0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9 and 1.0 is discussed. In particular, a comparison is made of the structural results obtained from an X-ray absorption spectroscopy (XAS) experiment and the corresponding data obtained in classical molecular dynamics (MD) simulations. In MD simulations, realized in the isobaric-isothermal (NpT) ensemble, the Dixon and Sangster's potential parameterisation (M. Dixon and M. J. L. Sangster, J. Phys. C: Solid State Phys., 9, 3381 (1976)) has been applied. The ability of the theoretical model of interatomic interaction to reproduce the structural properties observed in the EXAFS experiment is critically discussed.

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Short- and medium-range order in bismuth-silicate glasses: a solecular dynamics study

Witkowska A., Rybicki J., Laskowski R., Mancini G., Feliziani S., Alda W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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1999

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Vol. 3, No 2

239-254

EN

We report on the results of classical molecular dynamics (MD) simulations of str ucture of amorphous 15 Bi2O3 85 SiO2 [% mol] and 40 Bi2O3 60 SiO2 [% mol], and their totally reduced forms, 15 Bi2 85 SiO2 [% mol], and 40 Bi2 60 SiO2 [% mol], respectively. The simulations have been perfo rmed in the isobaric-isoenthalpic ensemble, using a two-body interaction potential. The set of the potential parameters was constructed as a suitable com bination of the parameters which were previously proposed for pure Bi2O3, and SiO2. Both unreduced, and reduced sy stems were initially prepared as well equilibrated hot melts, and then slowly co oled down to 300K. The structural information from the MD simulations was obtained from radial and angular distribution functions, static structural factors, Voronoi polyhedra sta tistics, and ring analysis. The simulation results can be summarised as follows. In unreduced glass with 15% [mol] Bi2O3 contents, the silicon structural units (mainly regular tetrahedra) form continuous network, whereas in 40% [mol] Bi2O3 glass these units are disconnected. In both unreduced systems Bi ions have mainly six-fold oxygen co-ordination, and no dominating structural unit can be individuated. However, the distorted bismu th units form a continuous network. In both totally reduced glasses (15% Bi2 85% SiO2, and 40% Bi2 60% SiO2 [% mol]), the silica network is built entirely from corner shari ng SiO4 tetrahedra. The structure of the silica subsystem is similar to that of pure *-SiO2. After the reduction, the Bi-Bi co-ordination significantly increases, whereas the first neighbour distance decreases. Moreover, partial static structural fact ors for Bi-Bi pairs indicate that the medium-range order in reduced glasses exhi bits greater periodicity than in unreduced glasses. Neutral Bi atoms form small clusters within the silica matrix.

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Molecular dynamics study of temperature-induced structural changes in YBa2Cu3O7 crystal

Bośko J., Sadowski W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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1999

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Vol. 3, No 3

293-302

EN

The structure of YBa2Cu3O7 crystal has been studied with the aid of molecular-dynamics (MD) technique. A two-body model potentials proposed by Zhang and Catlow have been used in MD simulations performed in wide range of temperature. The temperature-induced orthorhombic-to-tetragonal phase transition is observed. The distruction of the arrangement of atoms in the CuO chains due to diffusion of oxygen atoms is observed. The diffusion coefficients are calculated, and their variation as a function of temperature is analysed. The activation energy is estimated.