The quasirelativistic contact interaction and effective electron and spin densities at the nucleus: A model based on weighting the electron density with the finite Gaussian nucleus model

The Infinite Order Two Component quasirelativistic Hartree–Fock contact and effective electron/spin densities of Cu, Ag, Au atoms and the chemical shifts of HgF2, Cu+, Ag+ and Au+ are presented. The effective densities for the Gaussian nucleus model based on the weighted product of electron/spin density with the Gaussian distribution of the nucleus are reported for the first time. The effective (average) electron density obtained via the derivative of the energy of the system with respect to the size of the nucleus is shown for comparison. The finite-field difference method to obtain the derivative of the energy is also considered.