Formation mechanism of the (2 x 1) reconstruction of calcite (104)

TL;DR

This study uses density functional theory to elucidate the atomic and electronic mechanisms behind the (2x1) reconstruction of calcite (104), revealing that increased surface atom coordination drives the process.

Contribution

It provides a detailed atomic-level understanding of calcite (104) surface reconstruction, highlighting the role of coordination number increase and stability factors.

Findings

Reconstruction increases Ca-O bonds by four per unit cell.

Both unreconstructed and reconstructed surfaces are dynamically stable.

An energy barrier exists during the reconstruction process.

Abstract

Calcite has recently attracted extensive research interest in fields ranging from geoscience to carbon dioxide removal. Although much effort has been made to study the (2x1) reconstruction of the most stable (104) surface, the origin of this reconstruction remains unclear. Here, we carefully investigate the atomic and electronic structures of calcite (104) via density functional theory methods with van der Waals corrections. The results unambiguously show that the driving force for this reconstruction is the intrinsic demands of surface atoms to increase the coordination numbers. On reconstructing, calcite (104) forms four additional Ca-O bonds per (2x1) unit cell. Besides, phonon spectrums indicate both unreconstructed and reconstructed surfaces are dynamically stable. Finally, by applying the climbing image nudged elastic band method, an energy barrier is predicted during the reconstructing. This work delivers a full picture for the formation of calcite (104)-(2x1) reconstruction and can greatly advance the understanding of surface science for calcite.