Separation of sigma and pi energies

This work presents an all-electron density functional theory implementation of the separation of sigma and pi energies. On the basis of the separation of the electronic density, rho, into sigma and pi parts, an ansatz for the separation of the exchange-correlation energy is proposed. The behavior of the sigma and pi energy parts in benzene is investigated under different distortions. The effect of local and nonlocal functionals on the separation of the exchange-correlation energy is studied, too.