Computational Chemistry
Software YellowPages

SIRPOW

A. ALTOMARE, G. CASCARANO, C. GIACOVAZZO, A. GUAGLIARDI Istituto di Ricerca per lo Sviluppo di Metodologie Cristallografiche CNR, c/o Dipartimento Geomineralogico, Campus Universitario, 70124 Bari, Italy,

M.C. BURLA, G. POLIDORI Dipartimento di Scienze della Terra, Universita', 06100 Perugia, Italy,

M. CAMALLI Ist. di Strutturistica Chimica "G. Giacomello", CNR, Via Salaria Km 29,200, 00016 Monterotondo stazione (Roma), Italy.

THE CRYSTALLOGRAPHIC PROBLEM: Solving crystal structures from powder data is not a routinary job: peak overlapping, preferred orientation and difficulties in background estimation make uncertain the evaluation of the diffraction intensities for the various reflections. Consequently both Patterson and direct methods lose efficiency and structure solution is not straightforward. The first aim of this program is to optimize direct methods for powder data.

METHOD OF SOLUTION: The standard input of SIRPOW.92 consists of lattice constants, space group, chemical content of the unit cell, and a file of reflections as provided by current peak decomposition programs. Neutron data as well as X-ray data can be managed. The overlapping conditions, chosen by the program or fixed by the user, are stored for subsequent use. For example, /E/'s of some "important" overlapping reflections can be suitably varied in order to generate different phasing pathways. As in SIR92 (Altomare, Cascarano, Giacovazzo, Guagliardi, Burla, Polidori & Camalli, 1994) 1-phase and 2-phase structure seminvariants and 3- and 4-phase structure invariants are estimated via proper representations (Giacovazzo, 1977, 1980). Trial solutions are obtained by the magic integer approach (Main, 1978) or by random phases (Baggio, Woolfson, Declercq & Germain, 1978). The best solution, selected by proper FOM's, is automatically processed through a cyclic procedure integrating structure factor calculation - least squares - 2Fo-Fc Fourier synthesis. Due to reflection overlap the observations in the least squares routine are the total intensities of groups of reflections, while intensities of single reflections constitute single observations only when they do not overlap with any other. The final outcome is a set of refined atomic parameters (x,y,z) associated with atomic species. When neutron data are processed parameters of atomic species with negative scattering length can also be determined. If a graphic device is available the user can follow structure solution and refinement on the screen. In the final stage a menu-driven interface is available in order to study molecular geometry and restart refinement. Due to the small ratio "number of observations / number of parameters" the residual R values must be carefully considered by the user (usually final values between 0.06 and 0.20).

SOFTWARE ENVIRONMENT: The program has been written in standard Fortran77. A module written in C language is supplied in order to interface the program with X-window or DEC-Window terminal for graphics. Therefore, besides a C compiler, an Xlib library is also needed. Two ASCII files are associated to the program: the first contains coefficients for calculating scattering factors, the second, necessary for graphics, contains on-line help.

HARDWARE ENVIRONMENT: The program runs on UNIX and DEC workstations, on mainframe and on personal computers (for this last one 4 Mbytes of RAM and a VGA monitor are needed).

PROGRAM SPECIFICATION: The source code of the program consists of 44.000 FORTRAN lines and of 2000 C lines (including comments).

DOCUMENTATION: Users instructions and program description (about 1400 lines) are supplied as an ASCII text file.

AVAILABILITY: The program is available free of charge from the teams in Bari and in Perugia. A licence agreement has to be signed.

To obtain a copy please contact Dr Cascarano providing your ftp address.

Dr. Gianluca Cascarano
Istituto di Ricerca per lo Sviluppo di Metodologie
Cristallografiche CNR
c/o Dipartimento Geomineralogico
Campus Universitario
70124 Bari, Italy
Tel: +39-80-242624
FAX: +39-80-242591
E-mail: cryst@arba.ba.cnr.it

REFERENCES

Altomare, A., Cascarano, G., Giacovazzo, C., Guagliardi, A., Burla, M.C., Polidori, G. & Camalli, M. (1994). J. Appl. Cryst. 27,000-000.

Baggio, R., Woolfson, M.M., Declercq, J.P. & Germain, G. (1978). Acta Cryst. A34,883-892.

Giacovazzo, C. (1977). Acta Cryst. A33,933-944.

Giacovazzo, C. (1980). Acta Cryst. A36,362-372.

Main, P. (1978). Acta Cryst. A34,31-38.



NetSci, ISSN 1092-7360, is published by Network Science Corporation. Except where expressly stated, content at this site is copyright (© 1995 - 2010) by Network Science Corporation and is for your personal use only. No redistribution is allowed without written permission from Network Science Corporation. This web site is managed by:

Network Science Corporation
4411 Connecticut Avenue NW, STE 514
Washington, DC 20008
Tel: (828) 817-9811
E-mail: TheEditors@netsci.org
Website Hosted by Total Choice