Determination of the Electric Dipole Moment of a Molecule from Plane-Wave Density Functional Theory Calculations

The dipole moment calculated by using density functional theory (DFT) calculations varies, sometimes by a factor of 2, depending on the choice of the basis functions. We choose a plane-wave basis and calculate the electric dipole moment of a molecule by using the differential electron density with respect to the superimposed electron density of the free atoms, exploiting the cancellation of errors. Our results for a range of molecules show excellent agreement with experiments.