Geometric structures, energetics, and electronic properties of single-layer sheets, multilayer stacks, and single-walled nanotubes (SWNTs) of cadmium chalcogenides CdX (X = S, Se, Te) have been studied using ab initio density functional theory, along with spin–orbit coupling, van der Waals (vdW) interactions, and the GW approximation. Methodologies applied to the rationally designed materials have been validated through the experimental structural parameters and band gaps of 3D bulk zinc blende and wurtzite phases of CdX. The 2D single-layer sheet of CdS is found to be completely planar, while those of CdSe and CdTe are slightly corrugated, all showing a honeycomb lattice. The 2D sheets are destabilized with respect to the bulk zinc blende and wurtzite phases, but can be significantly stabilized by forming 3D multilayer stacks as a result of interlayer interactions. 1D (5,5) armchair and (9,0) zigzag SWNTs are also stabilized from their single-layer sheet counterparts. Both SWNTs consist of two concentric cylinders, with the Cd and X atoms in the inner and the outer cylinders, respectively, and with the intercylinder separations showing the same trend as the degree of nonplanarity in the single-layer sheets. By analogy to quantum dots of CdX, we suggest quantum flakes as interesting targets for experimental synthesis due to the diverse band gaps complementary to those of the bulk phases, allowing a much wider wavelength range, from infrared, visible, to ultraviolet, to be utilized.