Monopole polarization of C60 fullerene shell

TL;DR

This paper investigates the electrostatic charge distribution in C60 fullerenes, critiques common modeling approaches, and proposes a new potential model that better captures the shell's monopole polarization, with implications for photoionization calculations.

Contribution

It introduces a hyperbolic cosine potential model for C60 polarization, improving upon the traditional square-well approach and demonstrating its effects on photoionization.

Findings

Square-well potential leads to nonphysical charge densities.

Modified Coulomb-like potential does not accurately describe interior polarization.

The new hyperbolic cosine potential effectively models monopole polarization.

Abstract

We analyze using Poisson equation the spatial distributions of the positive charge of carbon atomic nuclei shell and negative charge of electron clouds forming the electrostatic potential of the C60 fullerene shell as a whole. We consider also the case when an extra positive charge appears inside C60 in course of e.g. photoionization of an endohedral A@C. We demonstrate that frequently used radial square-well potential U(r) simulating the C60 shell leads to nonphysical charge densities of the shell in both cases - without and with an extra positive charge inside. We conclude that the square well U(r) modified by adding a Coulomb-potential-like term does not describe the interior polarization of the shell by the electric charge located in the center of the C60 shell. We suggest another model potential, namely that of hyperbolic cosine shape with properly adjusted parameters that is able to describe the monopole polarization of C60 shell. As a concrete illustration, we have calculated the photoionization cross-sections of H@C60 taking into account the monopole polarization of the shell in the frame of suggested model. We demonstrate that proper account of this polarization does not change the photoionization cross-section.