DISCUS: a program for diffuse scattering and defect-structure simulation

Abstract

The program DISCUS is a versatile tool for the analysis of diffuse scattering and for defect structure simulations. The model structure can be created from an asymmetric unit of a unit cell or a complete structure can be read from a file. A Fortran77 style interpreter that includes IF statements and various loops combined with predefined defect types like thermal displacements, waves and microdomains allows one to create all sorts of defect structures. The Fourier-transform segment of the program allows one to calculate neutron as well as X-ray intensities including isotropic temperature factors and anomalous scattering. The calculation of the inverse and difference Fourier transform as well as the Patterson function is also implemented. A model structure can be 'fitted' to observed diffuse scattering data by reverse Monte Carlo (RMC) simulations. The RMC segment allows one to model displacive as well as occupational disorder. The program is completely written in Fortran77 and the source code is available via the World Wide Web.

In situ solid-state NMR and XRD studies of the ADOR process and the unusual structure of zeolite IPC-6

“…4 Previously reported Rietveld refinement of IPC-6 shows that the average structure is a disordered arrangement of 50% OKO connections and 50% PCR, but provides no information about how the different layers are stacked relative to each other (as Rietveld analysis only gives a bulk average). 4 To address this issue we prepared simulated crystallites with different possible stacking sequences using DISCUS 13,14 and calculated their PXRD patterns to compare with experiment ( Figure 4) as already demonstrated for AEI/CHA intergrowth structure. 14,15 The most obvious possibility for the IPC-6 structure is a random intergrowth between the IPC-4 and IPC-2 structures.…”

“…The PXRD patterns derived from the crystal structures of IPC-4 (PCR framework), OKO (IPC-2) and IPC-6 were modelled using the DISCUS 13,14 program, operating in stacking fault mode. The basic structural units used were: IPC-4 based layer (type A) and IPC-2 based layer (type B).…”

PDFgetN: a user-friendly program to extract the total scattering structure factor and the pair distribution function from neutron powder diffraction data

“…They can be automatically reloaded into PDFgetN for further analysis. The ®le format is compatible with the PDF modeling programs PDFFIT and DISCUS (Proffen & Billinge, 1999;Proffen & Neder, 1997), but the¯exible format means that S(Q) and PDF data can be easily exported to other packages. The data analysis programs that are called by PDFgetN are derived from the GLASS package (D. L. Price, internal report) and have been described by Billinge (1993).…”

Ближний порядок в магнитомягком сплаве alpha-FeAl

“…Особенности диффузного рассеяния в сплавах Fe-Si объяснялись присутствием кластеров, состоящих из двух ОЦК-ячеек, которые центрированы атомами кремния и имеют общую грань. Моделирование структуры, состо-ящей из хаотично ориентированных кластеров B2-типа, окруженных деформированными ОЦК-ячейками железа, давало хорошее (на качественном уровне) согласие расчетных и экспериментально наблюдаемых картин диффузного рассеяния [55,64].…”

“…6, поэтому не приводится. Для проверки справедливости предположения о том, что диффузные пики, смещенные в направлении мень-ших углов рассеяния из узлов с нечетной суммой индексов, являются вкладами от деформированных об-ластей B2-фазы, были проведены модельные расчеты с помощью пакета программ DISCUS [64]. Для этого сначала моделировалась ОЦК-решетка кристалла, содер-жащая деформированные кластеры, т. е. пары имеющих общую грань ОЦК-ячеек, с упорядочением B2-типа, аналогично тому, как это делалось в наших исследова-ниях железокремнистых магнитомягких сплавов [55,66].…”