The datasets include the input and output files to calculate the total energy and excited state energy of finite carbon chains terminated by hydrogen (oligoynes) and infinite carbon chain (polyyne) using quantum Monte Carlo (QMC) and Density functional theory (DFT). Folders called hse06_functional and pbe_functional are the type of exchange correlation functional used to relax the geometries and calculate DFT and QMC energies. All the required pseudopotentials are provided in the pseudopotentials folder. Carbon chain folder also includes additional DMC optimised lattice parameter and DMC bond length alternation as well as phonon calculations. For easier following calculations, we have added a brief description into each input.