Diffraction indicates varied cellulose Iβ unit cell dimensions. Reasons include relatively weak van der Waals forces along the unit cell a-axis and varying crystallite dimensions. Although a crystal structure is available for large-crystal tunicate cellulose , there is less information about commercial cellulose structures with smaller crystallites. This is a problem for application of the Rietveld method for analyzing the diffraction patterns for the details of crystallinity, size, and structure.For cellulose, the Rietveld method  reports what changes to the model tunicate structure are needed to make its calculated diffraction pattern match the observed pattern. The model is modified by refining the important variables: background, crystallite size and size anisotropy, unit cell dimensions, amorphous content and non-random orientation of the crystallites in the sample holder. Rietveld could determine individual atomic positions, but the limited data from cellulose powders is already overtaxed by these important variables. When the MAUD  Rietveld software changes the unit cell dimensions, it compresses or stretches molecular structures without rotation. Such refinements could lead to structures with high calculated energy, in part because the tunicate structure might be distant from the correct structure. To gain insight, we used Quantum Espresso  software to vary the a- and b-axis lengths and theγ angle. Results for unit cells with the shortest axes were about 36 kJ above the minimum energy structure.