Effect of Self-Interaction Correction on Molecular Polarizabilities and Core Ionization Energies
Density Functional Theory (DFT) is one of the most successful and popular computational Quantum Mechanical approaches to understanding materials. DFT allows the prediction of material properties from the electron density. Although in principle, density functional theory is exact, it, however, relies on approximate functional for exchange-correlation energy. Due to the approximate nature of the exchange-correlation functional, the self-Coulomb energy of the electrons is not exactly canceled out by the self-exchange, leading to the spurious self-interaction error (SIE). Due to this error, the potential shows incorrect behavior which leads to errors in calculated properties such as ionization energies, electron affinities, polarizabilities, band gaps, etc.The SIE can be removed in an orbital by orbital basis as given by the Perdew and Zunger in 1981 for local density approximation. In this work we applied Perdew-Zunger one electron self-interaction correction (SIC) and locally scaled SIC schemes to study the static dipole polarizabilities of different types of molecules. The polarizability is the response of a system to an applied electric field. However, due to the SIE, the density functional approximations tend to overestimate polarizabilities which is most apparent in long chain-like molecules. We applied the Perdew-Zunger SIC (PZSIC) and the locally scaled SIC (LSIC) methods to examine the polarizabilities of several different types of systems: the first and second-row atoms (H to Ar) from the periodic table, a set of small benchmark molecules, water clusters of sizes n=1-6,12, and polyacenes from benzene to pentacene. The PZSIC method tends to underestimate the polarizabilities. Pointwise scaling of the SIC with the LSIC method brings the polarizability values closer to the reference values.In the last project, we studied the core ionization energy of a series of molecules. In this project, we calculated the core-electron binding energies using DFAs with and without PZSIC for a series of molecules that includes the well-known ESCA (Ethyl trifluoroacetate) molecule and the Core-65 database molecules. The DFA eigenvalues underestimate the core ionization energies due to the self-interaction error. While PZSIC removes the SIE, the corrections are too large resulting in overestimation of the core-ionization energies. On the other hand, the total energy differences of the neutral and cation with PZSIC provide results with excellent agreement with experimental values. These applications bring out the effect of SIC on the density-related and the functional-related properties.
Akter, Sharmin, "Effect of Self-Interaction Correction on Molecular Polarizabilities and Core Ionization Energies" (2023). ETD Collection for University of Texas, El Paso. AAI30819617.