Molecular double core-hole electron spectroscopy for probing chemical bonds: C60 and chain molecules revisited

The double ionization energies of two-site double core-hole states were calculated for several systems: C-60, dicyano molecules, and disilyl compounds. For C-60, the interatomic relaxation energy decreases from positive to negative values with increasing core-hole distances. For dicyano molecules, the interatomic relaxation energy increases monotonically from a negative value toward zero with an increase in the carbon chain length. For disilyl compounds, the energy first decreases from positive to negative and then approaches zero with an increase in the carbon chain length. The results based on density functional theory agree with those based on Hartree-Fock theory for all systems, illustrating similar tendencies and confirming the validity of using density functional theory for calculations of double core-hole states. The origin of the different behaviors in interatomic relaxation energies is also discussed. (C) 2014 Elsevier B.V. All rights reserved.