Self-Interaction of Polarons Addressed through the Piecewise Linearity Condition

TH Department Seminar
Date: Feb 26, 2024
Time: 02:00 PM (Local Time Germany)
Speaker: Prof. Alfredo Pasquarello
Chaire de Simulation à l’Echelle Atomique, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Location: https://zoom.us/j/91361117903?pwd=Wk0zU204QldnU1J1b0gvSS9GMVhJZz09
Room: Meeting ID: 913 6111 7903 | Passcode: 677098
Host: TH Department

The piecewise linearity condition is a property satisfied by the exact density functional and has been found to yield band gaps in accord with experiment [1,2] when imposed to hybrid functionals.

Here, we address the self-interaction in relation to polarons in density functional theory. The self-interaction can be corrected focusing on its one-body form like it appears in Hartree-Fock theory or through the enforcement of the piecewise linearity condition, also referred to as the correction of the many-body self-interaction. We develop a unified theoretical framework encompassing one-body and many-body forms of self-interaction [3,4]. In this way, we establish a quantitative connection between the two forms of self-interaction, by which the many-body form is seen to account for the effect of electron screening [3,4]. In our investigation, we consider widely used functionals such as the global hybrid functional PBE0(α) [3-6], and the Hubbard-corrected functional DFT+U [5,6], as well as a newly developed semilocal scheme, called γ-DFT, which involves the use of a weak localized potential [3,4,6]. The enforcement of the piecewise linearity condition is achieved by imposing the generalized Koopmans’ condition to the neutral and charged states of the polaron upon proper consideration of finite-size effects induced by the lattice polarization [7]. The polaron properties are found to be robust upon variation of the functional, including charge densities [3-6], structural distortions [3-6], formation energies [3-6], energy barriers [6], hyperfine and superhyperfine parameters [6], and charge hopping rates [6].

[1] G. Miceli, W. Chen, I. Reshetnyak, and A. Pasquarello, Nonempirical hybrid functionals for band gaps and polaronic distortions in solids, Phys. Rev. B 97, 121112(R) (2018).
[2] J. Yang, S. Falletta, and A. Pasquarello, One-shot approach for enforcing piecewise linearity on hybrid functionals: Application to band gap predictions, J. Phys. Chem. Lett. 13, 3066-3071 (2022).
[3] S. Falletta and A. Pasquarello, Many-body self-interaction and polarons, Phys. Rev. Lett. 129, 126401 (2022).
[4] S. Falletta and A. Pasquarello, Polarons free from many-body self-interaction in density functional theory, Phys. Rev. B 106, 125119 (2022).
[5] S. Falletta and A. Pasquarello, Hubbard U through polaronic defect states, npj Comput. Mater. 8, 265 (2022).
[6] S. Falletta and A. Pasquarello, Polaron hopping through piecewise-linear functionals, Phys. Rev. B 107, 205125 (2023).
[7] S. Falletta, J. Wiktor, and A. Pasquarello, Finite-size corrections of defect energy levels involving ionic polarization, Phys. Rev. B 102, 041115(R) (2020).