Core-electron binding energies from self-consistent field molecular orbital theory using a mixture of all-electron real atoms and valence-electron model atoms

Abstract

The chemistry of large systems such as clusters may be readily investigated by valence-electron theories based on model potentials, but such an approach does not allow for the examination of core-electron binding energies which are commonly measured experimentally for such systems. Here we merge our previously developed Gaussian based valence-electron model potential theory with all-electron ab initio theory to allow for the calculation of core orbital binding energies when desired. For the atoms whose cores are to be examined, we use the real nuclear changes, all of the electrons, and the appropriate many-electron basis sets. For the rest of the system we use reduced nuclear charges, the Gaussian based model potentials, only the valence electrons, and appropriate valence-electron basis sets. Detailed results for neutral Al2 are presented for the cases of all-electron, mixed real–model, and model–model SCF–MO calculations. Several different all-electron and valence electron calculations have been done to test the use of the model potential per se, as well as the effect of basis set choice. The results are in all cases in excellent agreement with one another. Based on these studies, a set of ’’double-zeta’’ valence and all-electron basis functions have been used for further SCF–MO studies on Al3, Al4, AlNO, and OAl3. For a variety of difference combinations of real and model atoms we find excellent agreement for relative total energies, orbital energies (both core and valence), and Mulliken atomic populations. Finally, direct core-hole-state ionic calculations are reported in detail for Al2 and AlNO, and noted for Al3 and Al4. Results for corresponding frozen-orbital energy differences, relaxed SCF–MO energy differences, and relaxation energies are in all cases in excellent agreement (never differing by more than 0.07 eV, usually by somewhat less). Taken as a whole, the study clearly demonstrates the accuracy of the mixed real–model theory.