Jul 24, 1989 - of the Journal [J. Appl. Cryst. (1985). 18, 189-190]. J. AppL Cryst. (1989). 22, 640-641. XRAYL: a new powder diffrac- tion profile fitting program.
640
COMPUTER PROGRAM ABSTRACTS
Computer Program Abstracts
occurs it is necessary to separate the composite profile into its components. In practice, this can often be achieved using the technique of profile fitting. A computer program, XRAYL, has been developed to fit analytical functions to powder diffraction lines. The parametric profile functions implemented in XRAYL are: Gaussian, Lorentzian, Voigt, Pearson VII, and rational polynomial (Stewart, Zhang, Hubbard, Morosin & Venturini, 1988). In XRAYL, the asymmetric nature of powder diffraction profiles may be optionally modeled by using 'split' functions; that is, by using different profile parameters of the same functional form for each side of the peak. The 'split' functions, left side and right side, share the same peak maximum and peak positions. The full width at half maximum (FWHM) used in the intensity scaling for a split function is taken as the arithmetic mean of the left and right FWHM parameters. The calculation proceeds as follows: the data input files are read, the intensity data are stored in immediate access memory, and a survey is made of the starting parameters. Then, based upon the chosen function to be used in the fitting process, a Marquardt non-linearleast-squares fitting is carried out (Marquardt, 1963). In the least-squares refinement, the function minimized is [ W i ( I o i - Ici)2], where Ioi and Ici a r e the observed and calculated intensities at 20i, respectively, and wi is a weighting factor. The R values observed in the profile fitting using XRAYL have been as
The category Computer Program Abstracts provides a rapid means of communicating up-to-date information concerning both new programs or systems and significant updates to existing ones. Following normal submission, a Computer Program Abstract will be reviewed by one or two members of the IUCr Commission on Crystallographic Computing. It should not exceed 500 words in length and should use the standard format given on page 189 of the June 1985 issue of the Journal [J. Appl. Cryst. (1985). 18, 189-190].
J. AppL Cryst. (1989). 22, 640-641 XRAYL: a new powder diffraction profile fitting program. By J. M . S T E W A R T * a n d Y. Z H A N G ,
Department o f Chemistry, University o f Maryland, College Park, M D 2 0 7 4 2 , USA, C. R. HUBBARD, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 3 7 8 3 1 - 6 0 6 4 , USA, a n d B. M O R O S I N a n d E. L. VENTURINI, Sandia National
Laboratory,
Albuquerque,
NM
87185, USA
( Received 8 February 1989; accepted 24 July 1989) The crystallographic problem and method of solution: In many applications of powder diffraction, when overlap * T o whom correspondence and request for the software should be sent.
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Fig. 1. Example of profile fitting with XRAYL. See text for details.
0021-8898/89/060640-02503.00
Software and hardware environments: XRAYL, written in Fortran77, contains 5806 lines. It utilizes eight disk files for input and output. XRAYL has been well tested and run on a UNISYS 1100/92 (operating system 1100), a CYBER 855 and a CYBER 205 (operating system NOS 2.7.1 ) computer. These computers utilize 36, 60 and 64 bits per word respectively. While an overlay structure is used on the UNISYS (64 000 words), no overlay structure is used on the virtual-memory CYBER computers. In order to compile and to execute XRAYL, a least-squares routine, ZXSSQ, from the IMSL library is required. The subroutine library TEMPLATE, if available, can be easily integrated with XRAYL and this will give high-resolution plotting. However, XRAYL may also generate line-printer plots. Documentation and availability: A detailed document for XRAYL, including concepts, algorithms, operation, and execution examples is available (Stewart et al., 1988). Upon request, the source code of XRAYL, to be implemented on either UNISYS or CYBER, will be provided on either PC diskette or magnetic tape. Moreover, since XRAYL was designed to be transferable from machine to machine, it can also be implemented on other computers with minor modification of the source code.
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small as 0.3% on a peak with 211 points over 2.1 ° . After fitting, the powder diffraction data are represented, diffraction line by diffraction line, by parameters of a profile function. The resulting profile parameters may then be used to generate 'idealized' powder diffraction lines, effectively free of statistical noise and contributions from overlapping lines, extending to background intensity on each side. Because of this capability XRAYL may be employed in powder diffraction profile analysis as a preprocessor program, that is, separating peaks and feeding the 'resolved' data to subsequent analysis programs. Fig. 1 shows an example of the profile fitting using XRAYL. The material used in this example is GdBa2Cu3OT, a rareearth-based '123' high-T c superconductor (space group Pmmm, a=3.8466, b = 3.8958, c = 11.6794 A). In the pattern of this'material, there are several severely overlapped peaks. Fig. 1 shows the raw intensity versus 20 curve of the overlapped 013 and 103 lines, the composite Pearson VII curve, the fitting difference and the separated profiles.
References Marquardt, D. W. (1963). J. Soc. Ind. Appl. Math. 11, 2.
© 1989 International Union of Crystallography
COMPUTER PROGRAM ABSTRACTS Stewart, J. M., Zhang, Y., Hubbard, C. R., Morosin, B. & Venturini, E. L. (1988). Report NBS-IR 88-3850, pp, 127. National Institute of Standards and Technology, Gaithersburg, MD, USA.
Crystallographers This section is intended to be a series of short paragraphs dealing with the activities of crystallographers. such as their changes of position, promotions, assumption of significant new duties, honours, etc. Items for inclusion, subject to the approval of the Editorial Board. should be sent to the Executive Secretary of the International Union of Crystallography (J. N. King, International Union of Crystallography. 5 Abbey Square, Chester CH1 2HU, England).
J. AppL CrysL (1989). 22, 641
Bush Award for outstanding contributions to science and society. He has made major contributions to cryst.~lIography, molecular structure, chemical bonding, molecular biology and macromolecular evolution. Pauling was awarded the Nobel Prize in Chemistry in 1954 for research on chemical bonding and applications to chemical structure elucidation, and in 1962 he received the Nobel Peace Prize for his work on behalf of the international control of nuclear weapons and against nuclear weapons testing. The Vannevar Bush Award is named for the federal government official whose recommendation to President Truman resulted in establishment of the National Science Foundation in 1950.
Chin Hsuen Wei 1926-1989 Chin Hsuan Wei died on 7 January 1989, in Oak Ridge, Tennessee, after a yearlong struggle with amyotrophic lateral sclerosis, also known as Lou Gehrig's disease. Born in Yuanlin, Taiwan, Wei received his bachelor's degree in chemical engineering at Cheng Kung University in 1950, where he worked as an instructor until 1956. He received a scholarship for graduate studies at Purdue University, where he obtained a master's degree in 1958. From there he moved to the University of Wisconsin, Madison, where he obtained his doctorate in chemistry in 1962 with Lawrence F. Dahl. This was the beginning of a lifelong collaboration in the study of the structures of metal carbonyls and other metal-organic compounds. Wei published 25 papers on these materials, 17 of them co-authored by Dahl. In 1966 Wei went to the Biology Division, Oak Ridge National Laboratory, to work with J. Ralph Einstein. There he became an expert in biological protein chemistry. He wrote 14 papers on the purification, characterization, and crystallization of proteins, including the phytotoxins ricin and abrin. He also published 25 papers on the structures of other organic molecules including compounds related to photodimers of thymine and to the antischistosomal agent hycanthone. Of these papers, 15 were co-authored by Einstein. Hsuan Wei was probably the hardest working scientist I have known, often putting in more than 80 hours a week of work on his beloved crystallography. He is survived by his wife, Sue Yue Wei, and by his son, Aguan Wei, and daughter, Lilian M. Wei. He will be missed. WILLIAM R. BUSING
Linus Pauling, 88, retired director of the Linus Pauling Institute of Science and Medicine, has been selected to receive the National Science Board's Vannevar
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