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DFT+U-TiO2_35_preprint.pdf (1.41 MB)
On the Use of DFT+U to Describe the Electronic Structure of TiO2 Nanoparticles: (TiO2)35 as a Case Study
Preprints are manuscripts made publicly available before they have been submitted for formal peer review and publication. They might contain new research findings or data. Preprints can be a draft or final version of an author's research but must not have been accepted for publication at the time of submission.
submitted on 29.04.2020 and posted on 30.04.2020by Angel Morales, Stephen Rhatigan, Michael Nolan, Frances Illas
One of the main drawbacks in the density functional theory (DFT)
formalism is the underestimation of the energy gaps in semiconducting materials.
The combination of DFT with an explicit treatment of electronic correlation
with a Hubbard-like model, known as DFT+U method, has been extensively
applied to open up the energy gap in materials. Here, we introduce a systematic
study where the selection of U parameter is analyzed considering two different
basis sets: plane-waves (PWs) and numerical atomic orbitals (NAOs), together
with different implementations for including U, to investigate the structural and electronic properties of a well-defined
bipyramidal (TiO2)35 nanoparticle (NP). This study
reveals, as expected, that a certain U
value can reproduce the experimental value for the energy gap. However, there
is a high dependence on the choice of basis set and, and on the +U parameter
employed. The present study shows that the linear combination of the NAO basis
functions, as implemented in FHI-aims, requires a lower U value than the
simplified rotationally invariant approaches as implemented in VASP. Therefore,
the transferability of U values between codes is unfeasible and not
recommended, demanding initial benchmark studies for the property of interest as
a reference to determine the appropriate value of U.