Two Computer Programs for the Simulation of X-Ray Diffraction Phenomena FONE is an interactive Fortran program which, for a one-dimensional structure, computes structure factam, the Fourier synthesis and the Patterson synthesis. Input consists of the unit cell length, the number of atoms in the cell, and the atomic number and position of each atom. Structure factors are computed from the analytical form of the hydrogen scattering factor weighted by the atomic number. An additional input parameter is the maximum index t o be used in the Fourier series. Variation of this parameter makes it possible to demonstrate the effect of truncation of the Fourier series in terms of both resolution and ripple. The output of the program consists of an assignment of all the Patterson vectors, alist of the A, R, F 2 and $ values associated with each term of the summations, and line printer plots of both the Fourier and Patterson functions. The scaling of these plots may be done either automatically or may be controlled by the user. The Patterson functions may be distributed to students as exercises in the interpretation of such vector maps. PRECES is a FORTRAN Droeram .. for the simulation of X-rav, orecession ohotoeraohs. The current version of the progrnm is not i n w r n r t w hut ma) he run from n termmnl. Since the mput does not in\,olve the frartmnnl roordinntes ot' I he otorns rhr difirncrrd mtcnsit~eivnnnlr be calculated. mly the prnltions g r f the sp8,tr. It rs therefore necersary m tdtnt~fv the 1.nuesymmrtry c,itherryital.Th~iapparsntshwtcmningcan be turnedtuadvantage by asking the student todcntify the expected symmetry of each photo simulation. Input consists of the Laue symmetry, the symmetry elements (in coded form) present in the crystal, the lattice constants and the X-ray wavelength. The program will eliminate symmetry elements which are inconsistent with the specified Laue symmetry. Output consists of nine photo simulations corresponding the 0, 1 , 2 levels for each principal crystal zone. The output is on the line printer with observed spots indicated by a printed character. Since the line printer output is not appropriate for non-orthogonal cells it is also possible to request output of the actual coordinates lin mm) of the observed soots. Finallv. ,. for those installations where a dotter is availahle.. omvision is made I'M htaining ourput from the plotter. Students have i
