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SUPERIMPOSE – a program for the unambiguous structural superposition of spatially related molecules, including macromolecules
Author(s) -
Diederichs K.
Publication year - 1994
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889894000920
Subject(s) - macromolecule , superposition principle , molecule , chemistry , biophysics , chemical physics , crystallography , physics , biology , biochemistry , quantum mechanics , organic chemistry
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 figures of merit (FOM's), is automatically processed through a cyclic procedure integrating structure-factor calculation, least-squares refinement and 2Fo-Fc Fourier synthesis. Owing to reflection overlap, the observations in the leastsquares 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 menudriven interface is available in order to study molecular geometry and restart refinement. Owing to the small number of observations/number-of-parameters ratio, the residual R values must be carefully considered by the user (usually final values are between 0.06 and 0.20). Software environment: The program has been written in standard Fortran77. A module written in C is supplied for interface with X-window or DECWindow terminals. Besides a C compiler, an Xlib library is also needed. Two ASCII files are associated with 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 main-frame and personal computers (at least 4 Mbytes of RAM and a VGA monitor are needed). Program specification: The source code of the program consists of 44000 Fortran lines and 2000 C lines (including