Incorrect diatomic dissociation in variational reduced density matrix theory arises from the flawed description of fractionally charged atoms

H. van Aggelen, P. Bultinck, B. Verstichel, D. Van Neck, P.W. Ayers
Physical Chemistry Chemical Physics (PCCP)
11 (27), 5558-5560


The behaviour of diatomic molecules is examined using the variational second-order density matrix method under the P, Q and G conditions. It is found that the method describes the dissociation limit incorrectly, with fractional charges on the well-separated atoms. This can be traced back to the behaviour of the energy versus the number of electrons for the isolated atoms. It is shown that the energies for fractional charges are much too low.