The spin populations of , CO and NO are shown in Table . These were obtained by spin population analysis of calculations performed using spin dependent DFT with a GGA for the exchange-correlation potential.
Table: System spin, spilling parameter and Mulliken populations for spin dependent calculations of diatomic molecules.
If we examine the results for CO, which is non-magnetic, we find that the results obtained from the spin population analysis agree well with those obtained using spin-independent population analysis (see Tables and ). The atomic charges differ by only 0.02e and the total overlap population, the sum of the spin up and spin down overlap populations, differs by only 0.01e. These small differences are probably due to the fact that the spin-independent calculations were performed using the LDA rather than a GGA in the spin-dependent case.
The total energy calculations correctly predict a spin of 1 for the ground state of which is paramagnetic. As expected, the population analysis of the resulting plane wave eigenstates shows that there is no net charge on the oxygen atoms and that the spin is symmetrically distributed. Interestingly, if we examine the overlap populations between the atoms we find that there is a depletion of the spin up population between the atoms and that the net bonding is due to a strong bonding interaction between the spin down electrons on each atom. Thus it can be seen that the spin up electronic population is concentrated near to the atoms.
The NO molecule has an odd number of electrons giving rise to a net electronic spin of . In this case we can see that there is a net transfer of 0.15 electrons from the nitrogen atom to the oxygen, giving rise to net spins of 0.15 and 0.35 on the oxygen and nitrogen atoms respectively. It may also be seen that the net overlap spin is in fact down with a magnitude of 0.21 .