# Real-space study of the optical absorption in alternative phases of silicon

## TL;DR

This paper presents a real-space method to analyze how different crystal structures of silicon affect optical absorption, focusing on the Si20 phase and identifying key electronic factors responsible for absorption changes.

## Contribution

The study introduces a novel real-space approach to link crystal structure variations with optical absorption in silicon phases, highlighting electronic factors influencing absorption.

## Key findings

- 83% of absorption differences are due to on-site energy reductions
- Increased hopping integrals contribute to absorption changes
- Focus on Si20 phase as a case study

## Abstract

We introduce a real-space approach to understand the relationship between optical absorption and crystal structure. We apply this approach to alternative phases of silicon, with a focus on the Si$_{20}$ crystal phase as a case study. We find that about 83% of the changes in the calculated low-energy absorption in Si$_{20}$ as compared to Si in the diamond structure can be attributed to reducing the differences between the on-site energies of the bonding and anti-bonding orbitals as well as increasing the hopping integrals for specific Si-Si bonds.