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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).

2

The structure of Pb-PbO-SiO2 glass via molecular dynamics simulation

Rybicki J., Witkowska A., Bergmański G., Mancini G., Feliziani S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2003

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Vol. 7, No 2

243-256

EN

The paper is dedicated to a molecular dynamics (MD) study of the structure of partially reduced lead-silicate glass of composition 1Pb 1PbO 1SiO2. The simulations have been performed in the constant volume regime, using a two-body potential (Born-Mayer repulsive forces, and Coulomb forces due to full ionic charges). The system was initially prepared as a well equilibrated hot melt, and then slowly cooled down to 300K. The information on short-range correlations were obtained in a conventional way (from pair and angular distribution functions), while the medium-range order was studied via cation-anion ring analysis. In the paper, the short- and medium-range order in the simulated system is discussed and compared with the structure of a glassy completely reduced system, i.e. 2Pb 1SiO2 and unreduced one, i.e. 2PbO 1SiO2 glass.

3

2D simulations of liquid percolation through model porous media: preliminary MD and DPD results

Rychcik M., Bośko J., Rybicki J., Alda W., Dzwinel W., Mancini G., Fioretti L.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2001

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Vol. 5, No 1

85-97

EN

In the paper we make a short overview of computer models based on particle approach, which can be suitable for the simulation of fluid flow through porous media. We concentrate on Molecular Dynamics (MD) and Dissipative Particle Dynamics (DPD) methods. We describe main features of our simulation programs, and present and discuss preliminary results of MD and DPD simulations of 2D fluid flow through a simple model rigid porous media. The paper aims at the evaluation of the applicability of MD and DPD methods for simulations of liquid flows in media of complicated geometry.

4

The structure of rarefied and densified PbGeO3 and PbGeO2 glasses : a molecular dynamics study

Rybicki J., Witkowska A., Bergmański G., Bośko J., Mancini G., Feliziani S.

Computational Methods in Science and Technology

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2001

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Vol. 7, nr 1

91--112

EN

The paper is dedicated to a molecular dynamics (MD) study of the structure of rarefied and densified lead-germanate glasses, of compositions PbGeO3 and PbGeO2. The simulations have been performed at constant volume for systems with densities of 3000, 4000, 5000, 6285 (normal density), 7000, and 8000 kg/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 300 K. 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. In the paper, the short- and medium-range order in the rarefied and densified glasses is discussed and compared with the structure of the PbGeO3 and PbGeO2 glasses at normal conditions.

5

A new program package for structural analysis of computer simulated solids

Bergmański G., Rybicki J., Mancini G.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2000

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Vol. 4, No 4

555-573

EN

The opportunity to gain detailed information on representative set of rings and chains of atoms is of great importance in the analysis of medium-range order in the computer simulated structures of solids. A new program package (ANELLI) for ring and chain analysis of computer simulated atomic structures is presented. The paper includes detailed description of input and output files. The package presentation is followed by exemplary results obtained using our programs.

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Structure of rarefied PbGeO/sub 3/ glass: a molecular dynamics study.

Rybicki J., Witkowska A., Bośko J., Mancini G., Feliziani S.

Optica Applicata

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2000

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Vol. 30, nr 4

709-717

EN

The present contribution is dedicated to a molecular dynamics (MD) study of the structure of rarefied lead-germanate glasses of composition PbGeO/sub 3/. The simulations have been performed in the constant volume regime for systems with densities of 3000, 4000, 5000 and 6285 kg/m/sup 3/, using a two-body potential (Born-Mayer repulsive forces, and Coulomb forces due to full ionic charges). 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. In the paper the short and medium range order in the rarefied glasses is discussed and compared with the structure of the PbGeO/sub 3/ glass in normal conditions.

7

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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The structure of the first co-ordination shell of Pb atoms in lead - silicate glasses : a molecular dynamics study

Rybicka A., Rybicki J., Witkowska A., Feliziani S., Mancini G.

Computational Methods in Science and Technology

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1999

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Vol. 5

67-74

EN

The structure of lead-silicate glasses, although being investigated for over sixty years, rema ins still controversial. One of the open questions is the structure of the lead subsystem: what are the basic structural units like, and how are they interconnected. In the literature the appearance of [PbO4]n, or [PbO3]n chains is reported even in the glasses of the same stoichiometry. In order to elucidate the problem of contradicting experimental findings, extensive molecular dynamics (MD) simulations in the isobaric-isoenthalpic (NpH) ensemble of the structure of lead-silicate glasses have been performed in the whole range of glassformation. The atoms were assumed to interact by a two-body Born-Mayer-Huggins interaction potential with full ionic charges. The potential parametrization was taken from Damodaran et al. [Phys. Chem. Glasses, 31, 212 (1990)]. The simulation box contained about 3000 atoms. For each composition an equilibrated melt at 10000 K was prepared, and then slowly (6 ź 1013 K/s) cooled down to 300 K, passing several equilibrium states at intermediate temperatures. The simulation results can be summarised as follows. For 0.1 = x = 0.33, about ? of all Pb atoms is either placed in the front of the faces of the SiO 4 tetrahedra, forming PbO3 pyramids with the Pb atom in the vertices or in the middle of an almost flat triangle formed from apical oxygens of three different SiO 4 tetrahedra. Another ? of all Pb atoms can be qualified as vertices of rather distorted square pyramids. The remaining ? o f lead atoms have neighbourhoods difficult to classify. For x = 0.67 only a few Pb atoms were identified as remaining in the front of a face of a SiO 4 tetrahedron. Most of the Pb atoms are placed in the vertices of edge sharing square PbO4 pyramids. Our MD results are compared with available experimental data.