Core-ionized and core-excited states of macromolecules

Abstract

We report the calculation of core-ionized states of small organic compounds and macromolecular systems in the framework of a new method based on the local self-consistent field (LSCF). This new theoretical scheme avoids the variational collapse of the empty core orbital (CO) of the core-excited states and ensures the orthogonality between the ground state and the excited states. Compared to experimental data and other theoretical methods, accurate carbon 1s ionization energies using the Boys-Foster (BF) localization criterion for the determination of the CO and the PBE0/6-311++G**//B3LYP/ 6-311++G** level of theory was obtained to calculate both the ground and excited states. The macromolecular systems, a sequence of 15 alanine amino acids in both α-helix and β-sheet conformations, are computed using hybrid quantum mechanics/molecular mechanics (QM/MM) method within the LSCF/MM framework. The results show a weak impact of the MM surrounding in the alanine polypeptides cases compared with that of previous studies based on electrically charged residue, such as glutamate in the crambin protein. Show more