Electron density in Moller--Plesset theory

The Moller--Plesset theorem states that for the electronic Hamiltonian in the form H = summation/subp/F/subp/+V, where the eigenfunctions of F/subp/ are the Hartree--Fock molecular spin orbitals and the eigenvalues are the one-electron energies, by treating V as a perturbation the first order term in the expansion of the electron density vanishes. In spite of this, some one-electron properties are not given at the H--F level. This Note presents the expression for the second order correction to the electron density