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Structure recognition in MD-simulated materials. A case study of BO3 triangles in borate glasses

100%

Bergmański G. , Białoskórski M. , Rychcik-Leyk M. , Rybicki J.

tom Vol. 23, No. 4

989--999

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.

Model angular distribution functions in CA3, CA4 and CA6 structural units of glassy systems

100%

Bergmański G. , Feliziani S. , Rybicki J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

2007

tom Vol. 11, No 3

185-195

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.

Length distribution of fuzzy-end segments

88%

Frigio S. , Cosimi G. , Bergmański G. , Urbańska-Galewska E. , Rybicki J.

tom Vol. 10, No 3

291-309

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).

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

75%

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

tom Vol. 7, nr 1

91--112

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.