Unexpected softness of bilayer graphene and softening of A-A stacked graphene layers

Yiwei Sun, David Holec, Dominik Gehringer, O. Fenwick, David J. Dunstan, C.J. Humphreys

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung

6 Zitate (Scopus)


Density functional theory has been used to investigate the behavior of the π electrons in bilayer graphene and graphite under compression along the c axis. We have studied both conventional Bernal (A-B) and A-A stackings of the graphene layers. In bilayer graphene, only about 0.5% of the π-electron density is squeezed through the sp2 network for a compression of 20%, regardless of the stacking order. However, this has a major effect, resulting in bilayer graphene being about six times softer than graphite along the c axis. Under compression along the c axis, the heavily deformed electron orbitals (mainly those of the π electrons) increase the interlayer interaction between the graphene layers as expected, but, surprisingly, to a similar extent for A-A and Bernal stackings. On the other hand, this compression shifts the in-plane phonon frequencies of A-A stacked graphene layers significantly and very differently from the Bernal stacked layers. We attribute these results to some sp2 electrons in A-A stacking escaping the graphene plane and filling lower charge-density regions when under compression, hence, resulting in a nonmonotonic change in the sp2-bond stiffness.

FachzeitschriftPhysical review : B, Condensed matter and materials physics
PublikationsstatusVeröffentlicht - 20 März 2020

Bibliographische Notiz

Funding Information:
D.H. and D.G. gratefully acknowledge financial support under the scope of the COMET Program within the K2 Center “Integrated Computational Material, Process and Product Engineering (IC-MPPE)” (Project No. 859480). This program was supported by the Austrian Federal Ministries for Transport, Innovation and Technology (BMVIT) and for Digital and Economic Affairs (BMDW), represented by the Austrian Research Funding Association (FFG), and the federal states of Styria, Upper Austria, and Tyrol. The computational results presented have been achieved (in part) using the Vienna Scientific Cluster (VSC).

Publisher Copyright:
© 2020 American Physical Society.

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