SEMIEMPIRICAL CALCULATIONS OF THE ESCA CHEMICAL-SHIFTS OF NITROGEN-ATOMS IN A CHEMICAL ENVIRONMENT - FAILURE OF THE PM3-METHOD AND AM1-METHOD

The performance of the AM1 and PM3 semiempirical methods in calculatin g ESCA shifts in the inner-shell binding energies of the nitrogen atom is tested within the electrostatic potential model expressed in the a tomic monopole approximation. Relaxation energies accompanying the for mation of a positive highly localized inner hole by photoionization ar e estimated by the equivalent core approach. Both ESCA shifts and rela xation energies are in poor agreement with the experimental data and t he available ab initio results. A possible source of errors is detecte d in the screening zeta constants of the nitrogen atom AOs and its EC counterpart the oxygen atom, which are particularly unsatisfactory in the PM3 approach. A reparameterization of the PM3 and AM1 methods for nitrogen is therefore desirable. In contrast to the AMI and PM3 method s, the self-consisted charge method, which is based on the model hamil tonian and retains all overlap integrals, reproduces ESCA shifts and r eorganization energies in a satisfactory fashion.