Effects of exchange-correlation potentials on the density functional description of C_60 versus C_240 photoionization

TL;DR

This study compares how different exchange-correlation functionals in density functional theory affect the photoionization properties of C_60 and C_240 molecules, highlighting the importance of functional choice in modeling molecular responses.

Contribution

It introduces a comparative analysis of two xc functionals in DFT for modeling photoionization in large carbon molecules, emphasizing their impact on results.

Findings

Gradient-based xc potential yields results closer to experimental data for C_60.

Choice of xc functional significantly influences photoionization cross sections.

Molecular size affects the photoionization response and collective plasmon resonances.

Abstract

We study the photoionization properties of the C_60 versus C_240 molecule in a spherical jellium frame of density functional method. Two different approximations to the exchange-correlation (xc) functional are used: (i) The Gunnerson-Lundqvist parametrization [Phys. Rev. B 13, 4274 (1976)] with an explicit correction for the electron self-interaction (SIC) and (ii) a gradient-dependent augmentation of (i) by using the van Leeuwen and Baerends model potential [Phys. Rev. A 49, 2421 (1994)], in lieu of SIC, to implicitly restore electrons' asymptotic properties. Ground state results from the two schemes for both molecules show differences in the shapes of mean-field potentials and bound-level properties. The choice of a xc scheme also significantly alters the dipole single-photoionization cross sections obtained by an abinitio method that incorporates linear-response dynamical correlations. Differences in the structures and ionization responses between C_60 and C_240 uncover the effect of molecular size on the underlying physics. Analysis indicates that the collective plasmon resonances with the gradient-based xc-option produce results noticeably closer to the experimental data available for C_60.