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# Accurate Quantum Chemical Calculation of Ionization Potentials: Validation of the DFT-LOC Approach via a Large Data Set Obtained from Experiments and Benchmark Quantum Chemical Calculations

journal contribution

posted on 2020-03-20, 17:44 authored by Guangqi Li, Benjamin Rudshteyn, James Shee, John L. Weber, Dilek Coskun, Art D. Bochevarov, Richard A. FriesnerDensity functional theory (DFT) is known to often fail when calculating
thermodynamic values, such as ionization potentials (IPs), due to
nondynamical error (i.e., the self-interaction term). Localized orbital
corrections (LOCs), derived from assigning corresponding corrections
for the atomic orbitals, bonds, and paired and unpaired electrons,
are utilized to correct the IPs calculated from DFT. Some of the assigned
parameters, which are physically due to the contraction of and change
of the environment around a bond, depend on identifying the location
in the molecule from which the electron is removed using differences
in the charge density between neutral and oxidized species. In our
training set, various small organic and inorganic molecules from the
literature with the reported experimental IP were collected using
the NIST database. For certain molecules with uncertain or no experimental
measurements, we obtain the IP using coupled cluster theory and auxiliary
field quantum Monte Carlo. After applying these corrections, as generated
by least-squares regression, LOC reduces the mean absolute deviation (MAD) of the training set from 0.143
to 0.046 eV (

*R*^{2}= 0.895), and LOC reduces the MAD of the test set from 0.192 to 0.097 eV (*R*^{2}= 0.833).