Computational EPR Spectroscopy of Randomly Oriented Materials


Randomly oriented materials in form of powders, glasses or frozen solutions give
rise to EPR spectra that usually are not easily amenable to direct quantitative
analysis. In addition low symmetry environments often encountered in
disordered heterogeneous systems can further complicate the spectra. Under
such circumstances advanced computer analysis of the EPR spectra is the only
method suitable for accurate extraction of the spin Hamiltonian parameters,
allowing for their subsequent in-depth molecular interpretation. Computational
EPR spectroscopy provides a combination of a hybrid genetic algorithm for
robust and efficient simulation of complex experimental EPR spectra with
density functional theory (DFT) calculations of magnetic parameters (g and A
tensors or zero-field splitting). This approach can be used for guiding
interpretation of the EPR data of large molecular and reticular paramagnetic
systems characterized by complex structure, profound speciation, and low
symmetry features. Appropriate level of theory of the relativity treatment along
with careful selection of the exchange-correlation functional are indispensable
for obtaining sensible results. The trustful experimental EPR parameters may
guide the choice of proper calculation scheme to provide a quantitative
connection between the molecular structure of investigated paramagnets and
their spectroscopic fingerprints.
In this paper various aspects of computational EPR spectroscopy will be
discussed and illustrated using examples coming from our laboratory.

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