Physics and Chemistry of Molecular AssembliesMost researchers would relate X-ray structure analysis to crystal structure analysis. A crystal is a state in which atoms or molecules are regularly arranged in three-dimensional space. However, some substances do not have 3D structures, but have 1D, 2D, 1D⊕1D, 2D⊕1D or 1D⊕1D⊕1D structures. Here the symbol ⊕ stands for direct sum in linear algebra and is different from ordinary sum +. For example, 2D⊕1D means the direct sum of a 2D subspace and an orthogonal 1D subspace, not 3D.In a previous book, Physics and Chemistry of Molecular...