Simulating ionization spectra for small biomolecules in inner and valence shells

Accurate prediction of ionization spectra of biomolecules has been a challenge for theoretical spectroscopy. There is no single model which is the best for all biomolecules due to their diversity, leading to a variety of methods. Comparing to inner-shell, valence-shell ionization spectra have been studied more extensively [1-7]. Good agreement with experiment has been achieved from relevantly well developed models, such as the outer valence Green’s function (OVGF) model [8]. Energetics of a molecule are usually more sensitive to radial displacements rather than angular variations in the development of quantum chemistry in coordinate space. Energy differences among conformers of a biomolecule can be subtle, when the conformers are dominated by angular changes. However, such conformational changes can be significantly local, such as the shape of a particular orbital [2]. Dual space analysis (DSA) [9], is therefore applied to reveal details from both position space and momentum space of orbitals.