Moments of the electron momentum density: Requirements for ab initio and density functional theory calculations

Moments of the electron momentum density are calculated for 68 closed‐shell molecules in their ground states and equilibrium geometries. The computations are made with the Hartree–Fock (HF), Møller–Plesset (MP) perturbation theory, coupled cluster, and six density functional theory (DFT) methods, using a number of basis sets of contracted Gaussian‐type functions. Guidelines for the choice of basis sets for these properties are given. Electron correlation effects are found to be less than 8% and can often be accounted for by the second‐order MP method. DFT methods are found to give relatively poor results, often worse than the HF method. The coupled cluster results should provide a benchmark for future experiments and methodological developments.