Difference Fourier method

The structure of a-chitin was refined by using automatic, rigid, subunit, least-squares refinement and the difference-Fourier method. Two distinct types of statistical modification could be present in the structure, both of which would allow complete, intersheet hydrogenbonding between OH-6 groups within the general framework of Carlstrom s structure.56 The R factor is 22%. 

It is wise to remember that every operation, mathematical or physical, in real or reciprocal space has an equivalent operation in the other. Often these are not obvious, but they are always there. Molecular replacement, for example, can in theory be carried out in either space, though our computational tools for doing so are much more powerful in reciprocal space. Similarly, structure refinement may be carried out using least squares procedures in reciprocal space or, equivalently, difference Fourier methods in real space. 

E. Goldsmith, S. Sprang, R. Fletterick, Structure of maltoheptaose by difference Fourier methods and a model for glycogen J. Mol. Biol 156 1982, 411-27. 

---