4/2000 Advanced Methods of Structural Analysis

Contents:

• R.Laskowski, A new program for radical tessellation construction and analysis - abstract | full text
• G.Bergmanski, J.Rybicki and G.Mancini, A New Programme Package for Structural Analysis of Computer Simulated Solids - abstract | full text
• A.Filipponi and A.Di Cicco, GNXAS: a package of programs for advanced EXAFS multiple-scattering calculations and data-analysis - abstract | full text

Abstracts:

• R.Laskowski, A new program for radical tessellation construction and analysis

  The purpose of this work is to describe usage of computer program SIMPL designed for construction and analysis of radical tessellations of any computer simulated sample. The radical polyhedra (RP) [Gellatly B.J. and Finney J.L. 1982 J.Non-Cryst.Solids 50 313] can be considered as a generalization of the Voronoi polyhedra more widely used in literature. RP is a minimal polyhedron whose faces are sets of such points that distances from the points to tangent points of two neighboring atomic spheres are equal. The tessellation technique is a very efective tool for structural analysis of computer simulated samples, giving a great amount of easily accessible information. SIMPL allows to construct RP network for defined system and analyze shape, composition and mutual geometrical relation of radical polyhedra and radical simplices. Implemented capabilities give, for example, the posibility to recognize atomic environments' shape and investigate the non-local order in computer simulated materials. The pattern recognition technique [Laskowski R. et al. 1997 TASK Quart. 1 96] is based on analysis of the shape of the radical polyhedra, and contraction of short edges and small faces of the polyhedra. Non-local order analysis involves geometric relations between tessellation simplices.

• G.Bergmanski, J.Rybicki and G.Mancini, A New Programme Package for Structural Analysis of Computer Simulated Solids

  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. In the paper, 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.

• A.Filipponi and A.Di Cicco, GNXAS: a package of programs for advanced EXAFS multiple-scattering calculations and data-analysis

  Complete information about the GNXAS package of programs for advanced analysis of x-ray absorption spectroscopy (XAS) data is reported. These fortran programs are based on theoretical developments originally presented in Phys. Rev. B 52, 15122 and 15135, 1995). The GNXAS package is able to perform accurate multiple-scattering EXAFS (Extended X-ray Absorption Fine Structure) calculations of the x-ray absorption cross-section allowing reliable structural refinements of the short-range structure taking full advantage of the high-quality EXAFS data obtained using synchrotron radiation. The underlying philosophy, methodology, and the practical strategies used to develop and use the main crymol, phagen, gnpeak, gnxas, and fitheo codes are described in details. A detailed description of the necessary input data is given showing the practical usage of the GNXAS suite of programs for structural refinements and interpretation of raw XAS data. The problem of the estimation of statistical errors and of the treatment of XAS data of liquid and highly disordered systems is reported in details. A useful list of references to papers related to the development of the method and to applications in various scientific fields is given. The content of this paper can be regarded as a full documentation and guide for proper usage of the current version of the GNXAS software.