A faithful representation of the locations of the peaks of electron density maps can be obtained rapidly by determining for each point in the projected unit cell the algebraic sum of the amplitudes of those reflections which are contributing either a maximum or a minimum at each point. Since maxima and minima do not, in general, fall at the specific points of the grid, an approximation must be introduced. Using the semi‐polar form of Fourier series, the approximate summation can be accomplished with the use of one hundred and fifty strips. The method was tested by determining the peak locations in the structure of diopside projected on 001. Potential applications of the approximate summation include rapid checking of the validity of assumed crystal structures.
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