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1
Content available remote Model angular distribution functions in CA3, CA4 and CA6 structural units of glassy systems
Bergmański G., Feliziani S., Rybicki J.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2007
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Vol. 11, No 3
185-195
EN
We have calculated model partial angular distribution functions (pADFs) in CA3, CA4 and CA6 structural units, i. e. an equilateral triangle with three vertical anions, A, and a central cation, C, a regular tetrahedron with four vertical anions, A, and a central cation, C and a square bipyramid with six vertical anions, A, and a central cation, C. The model pADFs were calculated employing a simple Monte Carlo procedure: the ions were being shifted at random within 3D spheres of radius r with uniform probability density and the AAA, ACA and CAA angles were calculated for each random configuration. Repeating the calculation 10(8) - 10(9) times produced smooth probability densities for the angles' values. Conventional reference data so obtained can be applied to estimate the overall degree of deformation of the considered structural units in numerically simulated materials.
2
Content available remote Length distribution of fuzzy-end segments
Frigio S., Cosimi G., Bergmański G., Urbańska-Galewska E., Rybicki J.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2006
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Vol. 10, No 3
291-309
EN
We have calculated and discussed the probability density distributions of lengths of fuzzy-end segments, i. e. segments the ends of which assume random positions. We per-formed our calculations for several simple cases in 1, 2 and 3 dimensions: one end fixed, the other assuming a random position, and both ends at random positions. The obtained statistical data may serve as reference data for calculations of stochastic-geometrical properties of complex systems, such as conformations of complicated bolted construc-tions with clearances (in structure mechanics) or energy transfer processes between molecules in diluted systems (in physics).
3
Content available remote Structure recognition in MD-simulated materials. A case study of BO3 triangles in borate glasses
Bergmański G., Białoskórski M., Rychcik-Leyk M., Rybicki J.
Materials Science Poland
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2005
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Vol. 23, No. 4
989--999
EN
In computer simulations of the structure of matter, one usually obtains the Cartesian coordinates of all the particles involved. A non-trivial problem of structure recognition and characterization arises. In the present contribution, we study in detail the geometrical properties of a fuzzy-vertex CA3 structural unit (C - cation, A - anion). Two deformation degree estimators are introduced and examined. The Monte Carlo-generated stochastic characteristics of fuzzy CA3 triangles constitute conventional reference data that can be compared with the corresponding distributions calculated for a computer-simulated material. A quantitative estimation of the deformation degree of CA3 units in the simulated structure can thus be obtained. We apply the methods developed to quantitatively characterize the geometry of BO3 structural units in B2O3 glass.
4
Content available remote 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).
5
Content available remote The structure of porous and spontaneously densified amorphous PbSiO3 : a molecular dynamics study
Chomenko K., Bergmański G., Białoskórski M., Rychcik-Leyk M., Feliziani S., Frigio S., Witkowska A., Rybicki J.
Computational Methods in Science and Technology
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2004
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Vol. 10, nr 1
21-38
EN
In the paper we propose and test a "gel-drying" method of obtaining porous oxide glasses in Molecular Dynamics (MD) simulations. The simulation is started with low (screened) values of ionic charges. Then, the charges are gradually increased (to mimic the gradual elimination of a polar solvent) up to full ionic charges (a completely dry gel). This computational trick is applied to produce a porous PbSiO3 system. The structure of the resulting low-density samples is analysed in detail. Then, the porous structures are submitted to spontaneous densification, and the structure of the obtained dense bulk glasses is analysed. Finally, the structures of bulk glass obtained via spontaneous densification (density p - 8250 kg/m3) and bulk glass of the same density obtained via isotropic compression are compared.
6
Content available remote 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.
7
Content available remote A Molecular dynamics study of the influence of chemical reduction on the structure of amorphous germania
Witkowska A., Murawski L., Bergmański G.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2002
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Vol. 6, No 2
273-281
EN
The contribution is dedicated to the molecular dynamics (MD) study of the structure of reduced germania glass of composition 1Ge 1GeO2. The work is inspired by a recent report on the formation of Ge clusters in hydrogen reduced germanate glasses containing oxides of heavy metals. The MD simulations have been performed in the microcanonical (NVE) ensemble, using a simple two-body Born-Mayer-Huggins interaction potential. A tendency of germanium atoms to agglomeration into clusters, observed in the present calculations, is compared with an analogous tendency of Bi and Pb atoms, observed previously in the xBi (1-x)GeO2 and xPb (1-x)GeO2 systems. The differences in the short and medium-range order in GeO2 system between the 1Ge 1GeO2 and GeO2 glasses are discussed.
8
Content available remote 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.
9
Content available 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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