Predicting Core Level Photoelectron Spectra of Amino Acids Using Density Functional Theory

Core
level photoelectron spectroscopy is a widely used technique
to study amino acids. Interpretation of the individual contributions
from functional groups and their local chemical environments to overall
spectra requires both high-resolution reference spectra and theoretical
insights, for example, from density functional theory calculations.
This is a particular challenge for crystalline amino acids due to
the lack of experimental data and the limitation of previous calculations
to gas phase molecules. Here, a state of the art multiresolution approach
is used for high-precision gas phase calculations and to validate
core hole pseudopotentials for plane-wave calculations. This powerful
combination of complementary numerical techniques provides a framework
for accurate ΔSCF calculations for molecules and solids in systematic
basis sets. It is used to successfully predict C and O 1s core level
spectra of glycine, alanine, and serine and identify chemical state
contributions to experimental spectra of crystalline amino acids.