Showing papers in "Journal of Applied Crystallography in 1989"
TL;DR: NRCVAX is a complete system of programs, covering all aspects of crystal structure analysis from data reduction to the presentation of results, and it is usually safe to run the routines with a minimum of user input using the defaults.
Abstract: NRCVAX is a complete system of programs, covering all aspects of crystal structure analysis from data reduction to the presentation of results. The system, which is written in a `neutral' Fortran 77, presently exists in two forms. The first runs on a VAX computer under VMS, on an 80386 PC under UNIX and under IBM VM/CMS and MVS/TSO. The second is an adaptation which runs on PC-XT, AT, PS/2 and comparable microcomputers under MS-DOS. The two versions differ somewhat in structure, but very little in code, operation or functionality except for the graphics. The many options of the programs can be selected in a highly interactive manner and because of this the system is very flexible. Most options are assigned default values, however, and it is usually safe to run the routines with a minimum of user input using the defaults. The system will accept data from a wide variety of sources and has interface routines for several other systems. Graphics in the VAX/UNIX version are based on the widely available Tektronix 4000 series protocol, while the microcomputer version supports most common display adapters. It is also possible to prepare files for a variety of plotters, dot-matrix printers and laser printers. Source code is distributed and it should not be difficult to adapt the system to any computer with virtual memory and a Fortran 77 compiler.
1,357 citations
TL;DR: SIR88 as discussed by the authors is an integrated package of computer programs for the solution of crystal structures, based on the estimation of one-and two-phase structure seminvariants and three-and fourphase structure invariants according to the theory of representations.
Abstract: SIR88 is an integrated package of computer programs for the solution of crystal structures. The package is based on the estimation of one- and two-phase structure seminvariants and three- and four-phase structure invariants according to the theory of representations [Giacovazzo (1977). Acta Cryst. A33, 933–944; (1980). Acta Cryst. A36, 362–372]. The program works in all the space groups and in most cases it is able to provide the correct solution without user intervention. Some prior information like the availability of a partial structure or of pseudotranslational symmetry is easily exploited to obtain the structure solution.
769 citations
TL;DR: In this article, point-defect aggregates in (111) dislocation-free silicon single crystals grown by the float-zone (FZ) method have been studied by diffuse X-ray scattering (DXS) and compared with those in the Czochralski-grown (CZ) crystals.
Abstract: Point-defect aggregates in (111) dislocation-free silicon single crystals grown by the float-zone (FZ) method have been studied by diffuse X-ray scattering (DXS) and compared with those in the Czochralski-grown (CZ) crystals. A two-axis X-ray diffractometer was used. It employs three monochromators in (+, −, −) setting to obtain a highly collimated and monochromatic Mo Kα1 beam. DXS measurements were made around the 111 reciprocal-lattice point (r.l.p.) with K* along ±[111] and ±[01{\bar 1}]; K is the vector which joins the elemental volume of the reciprocal space under investigation to the nearest r.l.p. For FZ crystals for a given K* the DXS intensity was higher for θ θB showing that the anisotropy (DXS Iθ > θB − DXS Iθ < θB) is negative, as expected for vacancy clusters. For CZ crystals the anisotropy was positive, owing to the presence of interstitial clusters. The magnitude of anisotropy in the FZ crystals was smaller than that observed in the CZ crystals. The DXS intensity varies approximately as K−2 near Bragg peaks (Huang scattering) and as K*−4 (Stokes–Wilson scattering) away from it. From the K* values where the changeover from Huang to Stokes–Wilson scattering takes place the size of the clusters assumed to be the origin of the observed DXS is estimated as ~ 2 × 10−4 and 2.6 × 10−3 mm for FZ and ~ 5.5 × 10−4 and 3 × 10−3 mm for CZ crystals. The experimental data were compared with theoretically calculated DXS distributions assuming the defects to be dislocation loops. The number of point defects in a loop has been estimated.
348 citations
276 citations
TL;DR: Grazing-incidence small-angle X-ray scattering (GISAXS) is introduced as a method of studying discontinuous thin films in this paper, where the incident beam is totally externally reflected from the substrate followed by smallangle scattering of the refracted beam by the thin film.
Abstract: Grazing-incidence small-angle X-ray scattering (GISAXS) is introduced as a method of studying discontinuous thin films. In this method, the incident beam is totally externally reflected from the substrate followed by small-angle scattering of the refracted beam by the thin film. The experiment described establishes the ability of GISAXS to provide size information for islands formed in the initial stages of thin film growth. The data presented are for gold films of 7 and 15 A average thicknesses on Corning 7059 glass substrates. The advantages of this technique are that it is non-destructive, can be done in situ, provides excellent sampling statistics, does not necessarily require a synchrotron source, and is not limited to thin or conducting substrates.
276 citations
TL;DR: In this paper, the pole-figure inversion was used to calculate the orientation distribution function (ODF) of polycrystalline materials using the series-expansion method (harmonic method).
Abstract: The orientation distribution function (ODF) of the crystallites of polycrystalline materials can be calculated from experimentally measured pole density distribution functions (pole figures). This procedure, called pole-figure inversion, can be achieved by the series-expansion method (harmonic method). As a consequence of the (hkl)−({\bar h}{\bar k} {\bar l}) superposition, the solution is mathematically not unique. Rather it contains a range of possible solutions (kernel) which is only limited by the positivity condition of the distribution function. The complete distribution function f(g) can be split into two parts \tilde{f}(g) and \tilde{\tilde f}(g) expressed by even- and odd-order terms of the series expansions. For the calculation of the even part \tilde{f}(g), the positivity condition for all pole figures contributes essentially to an `economic' calculation of this part, whereas, for the odd part, the positivity condition of the ODF is the essential basis. Both of these positivity conditions can be easily incorporated in the series-expansion method by using several iterative cycles. This method proves to be particularly versatile since it makes use of the orthogonality and positivity at the same time.
233 citations
TL;DR: RAD as discussed by the authors is an interactive computer program for radial distribution analysis of X-ray diffraction data from amorphous materials, written in Fortran 77 and run on IBM PC/XT/AT or compatible computers.
Abstract: RAD is an interactive computer program for radial distribution analysis of X-ray diffraction data from amorphous materials. RAD has been written in Fortran 77 and runs on IBM PC/XT/AT or compatible computers.
205 citations
TL;DR: In this article, two time-of-flight powder diffractometers have operated at the Intense Pulsed Neutron Source (IPNS) since August 1981, and the performance of the two instruments is evaluated by analyzing data from a standard Al2O3 sample by the Rietveld method.
Abstract: Two time-of-flight powder diffractometers have operated at the Intense Pulsed Neutron Source (IPNS) since August 1981. These instruments use dedicated microcomputers to focus time-of-flight events so that data from different detectors can be summed into a single histogram. Thus, large multidetector arrays can be employed at any scattering angle from 12 to 157°. This design permits data to be collected over a uniquely wide range of d spacings while maintaining high resolution and count rates. The performance of the two instruments is evaluated by analyzing data from a standard Al2O3 sample by the Rietveld method. These instruments provide the capability for moderate- to high-resolution measurements with the duration of a typical run being a few hours.
202 citations
TL;DR: In this article, the authors used the SRS wiggler from a protein, pea lectin, and small-molecule crystals to record transmission Laue diffraction images.
Abstract: Transmission Laue diffraction photographs can be recorded with short exposure times from stationary macromolecular and small-molecule crystals. With the use of a broad wavelength band a very large number of reflections is stimulated in a single `snapshot' of large regions of reciprocal space. Processing software has been developed which allows quantitation of the Laue data without resort to monochromatic data. The procedures have been developed and the software strategies optimized by using test data recorded on the SRS wiggler from a protein, pea lectin, and small-molecule crystals. These latter include an organic molecule, trimethyl-1H-2,1,3-benzophosphadiazine-4(3H)-thione 2,2-disulfide, referred to as BPD, and a rhodium complex, [Rh6(CO)14(dppm)], where dppm is Ph2PCH2PPh2, referred to as RHCOP. Monochromatic data were available for comparison.
186 citations
TL;DR: In this article, a high-resolution multiple-reflection diffractometer was built to study crystals distorted by epitaxy and defects in nearly perfect crystals, which combines the merits of the two-crystal four-reflective monochromator and an analyser crystal to select the angular range diffracted from the sample crystal.
Abstract: A high-resolution multiple-reflection diffractometer has been built to study crystals distorted by epitaxy and defects in nearly perfect crystals. The diffractometer combines the merits of the two-crystal four-reflection monochromator (to define a narrow wavelength range with a tailless reflectivity profile) and an analyser crystal to select the angular range diffracted from the sample crystal. The diffractometer is operated in two modes. In the first the sample and analyser rotations are coupled to obtain near-perfect rocking curves from distorted crystals, and in the second mode the two axes are uncoupled to obtain a diffraction space map for studying the diffuse scattering. The simulation of these profiles and maps based on dynamical theory is presented. The former allows complex structures to be analysed and the latter case, by deconvolving the dynamical scattering in these maps, permits a complete interpretation of the kinematic scattering.
162 citations
TL;DR: An interactive program, POWD, written in Fortran77, for powder diffraction data interpretation and indexing is described, with very high success rates for indexing and tolerance of the presence of limited impurity lines.
Abstract: An interactive program, POWD, written in Fortran77, for powder diffraction data interpretation and indexing is described. Various functions such as the least-squares refinement and the systematic absence test are also included in this versatile program. The modified de Wolff figure of merit [Wu (1988). J. Appl. Cryst. 21, 530–535] is introduced in the program to decrease the execution time and estimate the reliability of the indexing. Very high success rates for indexing and tolerance of the presence of limited impurity lines are demonstrated by testing the program on several groups of powder data.
TL;DR: In this article, a method based on Rossmann's [J. Appl. Cryst. 12, 225,238] treatment of oscillation camera data for processing of X-ray diffraction data collected on a screenless Weissenberg camera for macromolecular crystals was developed.
Abstract: A method has been developed based on Rossmann's [J. Appl Cryst. (1979). 12, 225–238] treatment of oscillation camera data for processing of X-ray diffraction data collected on a screenless Weissenberg camera for macromolecular crystals [Sakabe (1983). J. Appl. Cryst. 16, 542–547]. Crystal orientation parameters and film orientation parameters are refined by minimizing the discrepancies between the calculated and observed positions of reflections on a film. A data processing example is presented. Intensities were collected using a synchrotron radiation source and the imaging plate as a detector. The results show that the quality of the data is good, as judged by the agreement of the equivalent reflections. An absorption correction based on the use of the empirical Fourier expansion method reduced the R value and improved the correlations between Bijvoet differences observed on the different imaging plate exposures.
TL;DR: Groma et al. as discussed by the authors used the Fourier transform of the line profiles of tensile-deformed Cu single crystals orientated for ideal multiple slip (IMS) to evaluate the dislocation structure.
Abstract: In paper I [Groma, Ung~ir & Wilkens (1988). J. Appl. Cryst. 21, 47-53] a theory was developed to interpret the asymmetric X-ray line broadening of plastically deformed crystals. It was shown that the dislocation structure can be described by five distinct parameters, namely the dislocation density, the mean quadratic spatial fluctuation of the dislocation density, the effective outer cut-off radius, the dipole polarization and the spatial fluctuation of the dipole polarization of the dislocation structure. In this paper a procedure is developed to evaluate these parameters from the Fourier transform of the line profiles. The theory and this procedure are tested by applying it to the asymmetric line profiles of tensile-deformed Cu single crystals orientated for ideal multiple slip. The asymmetry of these profiles is assigned to the dipole polarization of the dislocation cell structure and is directly correlated to residual long-range internal stresses. It is shown that the data can be interpreted in terms of the quasi-composite model of the dislocation cell structure developed earlier for the same material.
TL;DR: In this paper, a new approach is proposed, based on considering the contribution of each bilayer to the extinction in a given stack of bilayers, and the discrete equations governing the choice of layer thicknesses are derived and solved.
Abstract: Multilayer structures, analogous to broadband optical filters, may be used to reflect X-rays or neutrons at angles larger than the total external reflection angle intrinsic to the bulk mirror material. These so-called supermirrors have generally been designed using continuum theories, which predict that the thickness of the jth layer in the multilayer should vary smoothly as j−1/4. A new approach is proposed, based on considering the contribution of each bilayer to the extinction in a given stack of bilayers, and the discrete equations governing the choice of layer thicknesses are derived and solved. In the limit of zero layer thickness, the continuum result is recovered. The design produces essentially perfect reflectivity over the entire supermirror range. An optimal technique for trading reflectivity to gain angular range also emerges naturally from the physics of the design.
TL;DR: In this paper, drawings of molecular and solid-state structures generated by the computer program SCHAKAL88 are presented and some of the graphical techniques used for shading of line and raster drawings are briefly discussed.
Abstract: Drawings of molecular and solid-state structures generated by the computer program SCHAKAL88 are presented. Automatic atom labelling and some of the graphical techniques used for shading of line and raster drawings are briefly discussed.
TL;DR: In this article, a new apparatus is proposed for grazing X-ray measurements of thin films on flat substrates, where the multiple-beam interferences of parallel layers and/or the Bragg peaks of multilayers are measured in the angular dispersive mode with a position-sensitive proportional counter.
Abstract: A new apparatus is proposed for grazing X-ray measurements of thin films on flat substrates. The multiple-beam interferences of parallel layers and/or the Bragg peaks of multilayers are measured in the angular dispersive mode with a position-sensitive proportional counter. Measurements of thickness, densities and periodicities are easy to carry out on small sample areas in a much shorter time than with a classical goniometric recording. The principle, the design features and the resolution are described. Different examples showing the performance of the set-up are given.
TL;DR: In this article, a series of reflections were measured to obtain a representative picture of the dislocation-induced X-ray line broadening, and the integral breadths and the Fourier coefficients were evaluated by both direct profile-shape analysis and profile fitting with analytical functions.
Abstract: Procedures of X-ray diffraction line profile analysis for the evaluation of the dislocation content in plastically deformed hexagonal materials were tested by means of conventional powder diffractometry on polycrystalline zirconium deformed under tension at 77 K. In order to obtain a representative picture of the dislocation-induced X-ray line broadening a series of reflections was measured. The integral breadths and the Fourier coefficients were evaluated by both direct profile-shape analysis and profile fitting with analytical functions. The results show a significant anisotropy of the line broadening. The 0001 reflections are clearly less broadened than most of the others. According to the theoretical calculations presented previously such a phenomenon can be expected if the plastic deformation favours generation of dislocations with Burgers vectors a/3 〈2{\bar 1} {\bar 1}0〉.
TL;DR: In this article, the lattice parameters a and c and their ratio c/a vary linearly with x, and it is found that the composition of any chalcopyrite in the pseudo-binary system CuGaSe2 and CuInSe2 can be obtained from the accurate lattice parameter.
Abstract: The semiconducting compound CuGaxIn1 − xSe2 crystallizes in the chalcopyrite structure (space group I{\bar 4}2d, Z = 4). The X-ray powder data for x = 1, 0.75, 0.6, 0.5, 0.4, 0.25 and 0.0 have been collected and it is found that the lattice parameters a and c and their ratio c/a vary linearly with x. Thus the composition of any chalcopyrite in the pseudo-binary system CuGaSe2 and CuInSe2 can be obtained from the accurate lattice parameters. The crystallite size determined from the (112) plane is minimum for x = 0.50 (~ 1000 A) and away from x = 0.50 it increases. A value of u = 0.240 (5) has been established for fixing the Se-atom positions in the CuGa0.5In0.5Se2 solid solution. The JCPDS Diffraction File No. for CuInSe2 is 40-1487 and for CuGa0.5In0.5Se2 is 40-1488.
TL;DR: In this article, a new version of the Rietveld total-powder-pattern refinement method is introduced, which is applicable to neutron, synchrotron and conventional X-ray data when the incident radiation is essentially of one wavelength.
Abstract: A new version of the Rietveld total-powder-pattern refinement method is introduced. The profile function is true Voigtian and the Gaussian and Lorentzian components include broadening due to instrumental effects, particle size and strain and wavelength dispersion. The code is applicable to neutron, synchrotron and conventional X-ray data when the incident radiation is essentially of one wavelength. The effects of preferred orientation are included by expanding the orientation distribution in spherical harmonics. The harmonics are picked according to the Laue class, and the coefficients are the parameters being refined simultaneously with other parameters. X-ray measurements on Ni, Mg and NaNO3 are used as test data. The actual preferred orientation corrections are known for Ni and Mg from earlier measurements of radial pole figures. The corrections from the refinement agree very closely with the measured values, and different samples yield consistent results when preferred orientation is included in the model. Only a few terms of the harmonic expansion are needed for an adequate fit. The largest correction factors exceed 2, and in such cases the refinements without allowance for preferred orientation fail totally.
TL;DR: In this article, powder diffraction pattern and lattice parameters of the phases of CdI2 (2H, 12R, 4H), PbI2, SnS2, and SnSe2 were studied.
Abstract: Structural transformations between polytypes of a given material are expected to lead to lattice relaxations Powder X-ray diffraction of basic AX2 polytypes of CdI2, PbI2, SnS2 and SnSe2 showed these relaxations for the repetition unit along the stacking axis, conventionally the c axis No variation of the lattice parameters were detected in the basal plane (001), except for CdI2 where small variations occur also for the a lattice parameter The tensor of the spontaneous strain has its maximum component e3 ≲ 12 × 10−4 for SnS2 The powder diffraction pattern and lattice parameters of the phases of CdI2 (2H, 12R, 4H), PbI2 (2H, 12R), SnS2 (2H, 18R, 4H) and SnSe2 (2H, 18R) are given JCPDS Diffraction File Nos are: 40-1468 for CdI2-12H; 40–1469 for CdI2-2H; 40-1466 for SnS2-18R, 40–1467 for SnS2-2H; 40–1465 for SnSe2-18R The other polytypes studied in this paper have data in earlier sets of the PDF
TL;DR: A complete description of the current version of RESTRAIN, a program primarily for the least-squares refinement of macromolecular structures, and the version that will be released to the academic community is presented.
Abstract: A complete description of the current version of RESTRAIN, a program primarily for the least-squares refinement of macromolecular structures, is presented. This description announces the version that will be released to the academic community. The additional features present in this version are described in detail. The program is compared with two other macromolecular refinement programs. Finally information about documentation and availability is presented.
TL;DR: The method of crystallographic refinement using molecular dynamics has been implemented to work with the GROMOS simulation package and has been tested by applying it to the structure of phospholipase A2 as mentioned in this paper.
Abstract: The method of crystallographic refinement using molecular dynamics [Brunger, Kuriyan & Karplus (1987). Science, 235, 458–460] has been implemented to work with the GROMOS simulation package. It has been tested by applying it to the structure of phospholipase A2. The structure of this molecule had previously been refined at high resolution with conventional methods. The new method successfully refined the initial multi-isomorphous replacement structure, removing most of the errors, without any manual intervention. All the refinement was performed at 300 K. The use of lower-resolution data allows greater conformational transitions to occur whereas the inclusion of high-resolution data results in a more accurate structure.
TL;DR: In this paper, it is shown that with polymer fibres this causes serious errors in the normalization, and in the values of those low harmonics used in the size and disorder determination, and prevents reliable values being obtained.
Abstract: Methods which determine the number and disorder of lattice planes in a crystal from the Fourier cosine coefficients of the intensity profile of an X-ray reflection use only the low harmonics and require that the coefficients be normalized so that the zero harmonic is unity. Experimentally, the profiles can only be recorded over a smaller range of scattering angle than required by the theory, and it is necessary to subtract background, which is likely to be estimated with considerable error, before determining the coefficients. It is shown that with polymer fibres this causes serious errors in the normalization, and in the values of those low harmonics used in the size and disorder determination, and prevents reliable values being obtained. Methods which avoid normalization and use only high harmonics are needed. It is shown that disorder may be obtained in such a way, but not size, for which low-order normalized coefficients are essential. A method of extrapolation is described and tested which enables the accurate high harmonics to be used to improve the estimates of the low ones. Whilst this will yield more reliable values of crystal size than are obtainable from existing methods, the accuracy depends entirely on the validity of the extrapolation, which cannot be tested in many cases of interest.
TL;DR: In this article, the authors obtained convolutional products by folding a specimen-related function into another function representing the intrinsic profile of the diffractometer used in the study used in this paper.
Abstract: Convolution products Were obtained by folding a specimen-related function into another function representing the intrinsic profile of the diffractometer used in this study. The instrumental contributions were modeled with three split-Pearson VII functions: one for each of the a~, a2 and o~ 3 components in the Cu Ka spectral distribution. The positions and intensities of the a 2 and og 3 lines were based on those of the a~ line while their shapes were constrained to follow that of the a~. Values of the variable parameters of these functions, obtained from a 'defect-free' specimen, were fit with polynomials to establish four discrete curves from which the instrument profiles could be synthesized at any diffraction angle. Both a normalized Lorentzian and a Gaussian function were evaluated for use in representing the specimen contributions. The integral breadth (/3) of the specimen function was adjusted until the instrument-specimen convolution product best matched the observed profile. In specimens with small crystallite size, the angular dependence of/3 for the specimen profile followed the Scherrer relation while, in a strained specimen, the angular dependence followed the simple 4e tan 0 relation. In both cases, the specimen contributions were best modeled by a Lorentzian-type function.
TL;DR: In this paper, a lattice-dynamical model of β-cristobalite has been proposed, where the oxygen atoms are distributed uniformly around an annulus which encircles the 16(c) sites of the Fd3m C9 structure.
Abstract: A previously reported lattice-dynamical model of β-cristobalite [Hua, Welberry, Withers & Thompson (1988) J Appl Cryst 21, 458–465], which assumed the Wyckoff C9 structure but gave a satisfactory qualitative description of observed diffuse intensity in electron diffraction patterns, is shown to give atomic displacements which are much too small to be consistent with the 147° Si—O—Si angle observed in other forms of silica Monte Carlo simulations of a modified model in which this angle is constrained to be close to 147° have been carried out and optical diffraction patterns obtained from the resulting lattice realisations The diffraction patterns are very similar in appearance to those calculated for the simple C9 model, but the displacements are now consistent both with the expected geometry and also with mean-square atomic displacements derived from X-ray powder studies In this simulation the oxygen atoms are distributed uniformly around an annulus which encircles the 16(c) sites of the Fd3m C9 structure The hypothesis of Wright & Leadbetter [Philos Mag (1975) 31, 1391–1401], that the oxygen atoms preferentially occupy the six 96(h) sites which occur around this annulus, has been tested and it is concluded that if such ordering exists it is not very pronounced
TL;DR: In this article, the thermal expansion of five cubic zirconias of different yttria content were determined using high-temperature X-ray diffraction, and it was found that Yttria contents had no significant effect on thermal expansion.
Abstract: The thermal expansion of five cubic zirconias of different yttria content were determined using high-temperature X-ray diffraction. Yttria content was found to have no significant effect on thermal expansion.
TL;DR: A small position-sensitive 3He gas detector has been developed for diffraction studies using short-wavelength neutrons as mentioned in this paper, which has been used for standard data collection, as well as for studies of twinned crystals and measurements involving parasitic reflections.
Abstract: A small position-sensitive 3He gas detector has been developed for diffraction studies using short-wavelength neutrons. It covers 32 × 32 pixels with a 2 mm resolution, which in the present set up corresponds to 0.25°, and the efficiency is 75% at a wavelength of 0.8 A. The detector has been used for standard data collection, as well as for studies of twinned crystals and measurements involving parasitic reflections. In all cases it has improved the mode and speed of the measurement, with gain factors compared with single detectors which range from more than two in standard measurements to several hundred for the study of details of the Bragg peak(s). The computation time in data analysis and the storage of the data are no major limitations, partly due to the smallness of the data array, and partly due to efficient packing routines.
TL;DR: In this paper, the Rietveld method has been modified to incorporate line broadening from strains, particle size and microtwins, which has been applied to TiFeD1.9.
Abstract: The Rietveld method has been modified to incorporate line broadening from strains, particle size and microtwins. It has been applied to TiFeD1.9. The structure was determined to be orthorhombic [a0 = 7.0426 (2), b0 = 6.2371 (2), Co = 2.8315 (1) A] in space group Cmmm, in agreement with recent studies. The material is heavily twinned on the (110) planes with an average distance between twin planes of 24 ~.
TL;DR: In this paper, it was shown that when ammonium sulfate is used as the precipitant, pH changes occur due to ammonia transfer following ammonium/ammonia equilibrium.
Abstract: Possible pH variations during crystallization of biological macromolecules by the vapor diffusion method have not been taken into account in most experiments so far reported. The present study demonstrates that when ammonium sulfate is used as the precipitant, pH changes occur due to ammonia transfer following ammonium/ammonia equilibrium. The pH in a crystallization droplet is shown to be controlled by that of the reservoir. The theory of the effect is given and the consequences of pH variations during crystallization are discussed in terms of reproducibility of experiments. An application, the crystallization of concanavalin A induced by pH variation, is presented.
TL;DR: In this article, an automatic procedure for indexing reflections on oscillation photographs produced by crystals with very large unit cells (cell dimensions larger than about 100 A) was developed.
Abstract: An automatic procedure has been developed for indexing reflections on oscillation photographs produced by crystals with very large unit cells (cell dimensions larger than about 100 A). The procedure works in a similar fashion to the auto-indexing used in four-circle diffractometry. Features include ab initio cell parameter and orientation matrix determination, reduced cell calculation and transformation of the reduced cell to one with higher symmetry.