Effect Of Self-interaction Error Research Articles

First-principles calculation of the electronic and optical properties of Gd2FeCrO6 double perovskite: Effect of Hubbard U parameter

We have synthesized Gd$_{2}$FeCrO$_{6}$ (GFCO) double perovskite which is crystallized in a monoclinic structure with P2$_{1}/$n space group. The UV-visible and photoluminescence spectroscopic analyses confirmed its direct bandgap semiconducting nature. Employing experimentally obtained structural parameters in first-principles calculation, we report the spin-polarized electronic band structure, charge carrier effective mass, density of states, electronic charge density distribution and optical absorption property of the GFCO double perovskite. The effects of on-site d-d Coulomb interaction energy (U$_{eff}$) on the electronic and optical properties were investigated by applying a range of Hubbard U$_{eff}$ parameters from 0 to 6 eV to the Fe-3d and Cr-3d orbitals within the generalized gradient approximation (GGA) and GGA+U methods. When we applied U$_{eff}$ in the range of 1 to 5 eV, both the up-spin and down-spin band structures were observed to be direct. The charge carrier effective masses were also found to enhance gradually from U$_{eff} =$ 1 eV to 5 eV, but, these values were anomalous for U$_{eff} =$ 0 and 6 eV. These results suggest that U$_{eff}$ should be limited within the range of 1 to 5 eV to calculate the structural, electronic and optical properties of GFCO double perovskite. We observed that considering U$_{eff} =$ 3 eV, the theoretically calculated optical band gap 1.99 eV matched well with the experimentally obtained value 2.0 eV. The outcomes of our finding imply that the U$_{eff}$ value of 3 eV most accurately localized the Fe-3d and Cr-3d orbitals of GFCO keeping the effect of self-interaction error from the other orbitals almost negligible. Therefore, we may recommend U$_{eff} =$ 3 eV for first-principles calculation of the electronic and optical properties of GFCO double perovskite that might have potential in photocatalytic and related solar energy applications.

The effect of self-interaction error on electrostatic dipoles calculated using density functional theory.

Spurious electron self-interaction in density functional approximations (DFAs) can lead to inaccurate predictions of charge transfer in heteronuclear molecules that manifest as errors in calculated electrostatic dipoles. Here, we show the magnitude of these errors on dipoles computed for a diverse set of 47 molecules taken from the recent benchmark study of Hait and Head-Gordon [J. Chem. Theory Comput. 14, 1969 (2018)]. We compare the results of Perdew-Wang local spin density approximation (PW92), Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), and strongly constrained and appropriately normed (SCAN) meta-GGA dipole calculations, along with those of their respective self-interaction-corrected (SIC) counterparts, to reference values from accurate wave function-based methods. The SIC calculations were carried out using the Fermi-Löwdin orbital (FLO-SIC) approach. We find that correcting for self-interaction generally increases the degree of charge transfer, thereby increasing the size of calculated dipole moments. The FLO-SIC-PW92 and FLO-SIC-PBE dipoles are in better agreement with reference values than their uncorrected DFA counterparts, particularly for strongly ionic molecules where significant improvement is seen. Applying FLO-SIC to SCAN does not improve dipole values overall. We also show that removing self-interaction improves the description of the dipole for stretched-bond geometries and recovers the physically correct separated atom limit of zero dipole. Finally, we find that the best agreement between the FLO-SIC-DFA and reference dipoles occurs when the molecular geometries are optimized using the FLO-SIC-DFA.

The electron–ion dynamics in ionization of lithium carbide molecule under femtosecond laser pulses

The electron–ion dynamics of the linear lithium carbide molecule under femtosecond laser pulses have been investigated in the framework of Ehrenfest molecular dynamics, in which valence electrons are treated quantum mechanically by time-dependent density functional theory (TDDFT) and ions are described classically. The on- and off-resonant multiphoton ionization processes have been induced by regulating laser frequency and laser intensity. The laser pulse with on-resonant frequency induces pronounced enhancement in electron ionization, bond length vibration, and energy absorption. Moreover, the coulomb explosion is preferred to occur in the on-resonant case, which is in qualitative agreement with previous theoretical investigations. The subtle relations between escaped electron number and absorbed photon number are well discussed with the increasing of laser intensity. Finally, the effect of self-interaction error is analyzed by comparing escaped electron number calculated with LDA and LDA-ADSIC. And the revTPSS-meta-GGA, a currently more accurate nonempirical exchange–correlation energy functional from a point of static density functional theory, is introduced to display its capability for the description of ionization process within nonlinear and the nonperturbative regime of isolated systems.