SCF, CI and DFT Charge Transfers and XPS Chemical Shifts in Fluorinated Compounds

Ansatz for the evaluation of the relativistic contributions to core ionization energies in complex molecules involving heavy atoms

“…This is the reason why we choose to fit the relativistic corrections to the nonrelativistic energy rather than to the atomic number Z. Although these two are related in the atomic case 9, in the molecular case the shifts induced by the chemical environment of the ionized atom, mainly through the relative electronegativities of this atom and the bonded groups 1, 7, make Z partly irrelevant.…”

“…is the theoretical calculation of core excitation and ionization energies (CIEs) and their chemical shifts, experimentally measured in molecular systems or in condensed matter 1–3. In computing these properties, one has to take account of various effects: 1) electron correlation, particularly strong between inner‐core electrons 4, 5, which prevents the use of simple SCF schemes; 2) electron relaxation, which increases with the number of electrons 6–8, 9, preventing the use of simple Koopmans' theorem 10; 3) for systems involving heavy atoms, relativistic effects, which may overcome the previous effects in inner‐core excitations 8, 9, 12–14.…”

“…In previous articles we have proposed a procedure for evaluating core ionization / excitation chemical shifts in molecules from computed core ionization / excitation energies in the ionized / excited atom and charge transfers in the neutral molecule, the atomic calculation involving relaxation and, if appropriate, relativity 6–8. Ideally, one would like to make simple, Koopmans SCF (KSCF) evaluations (step 1) and deduce, from the approximate ionization/excitation energies thus obtained, exact values (step 4) by making use of some simple, appropriate formulae or tables, where corrective terms would appear in a parameterized function of the approximate value: In a first step, the problem can be split into including semiempirically, in this manner, either correlation, or relaxation, or relativity within an approximation comprising other contributions.…”