Van der Waals interactions and their impacts on the Raman spectra in two-dimensional layered atomic crystals

Abstract

Van der Waals (vdW) interactions in seven typical two-dimensional (2D) bilayer crystals, including
bilayer graphene, MoS₂, WS₂, phosphorene, TaSe₂, SnSe, and WS₂/MoS₂ heterostructure are
examined by first-principles calculations. While the local density approximation (LDA) predicts
a wide variety of binding energies ranging from 9 meV/angstrom² in bilayer graphene to 34 meV/angstrom² in
bilayer SnSe, calculations with vdW corrections at the vdW-DF2 level yield a universal binding
energy:  about 19 meV/angstrom², in close agreement with previous report. A detailed analysis of the charge
density redistribution induced by the interlayer coupling reveals a dramatic dierence predicted
from LDA and vdW-DF2 among these layered systems, which span from semiconductors, semimetals
to metals. Finally, effects of interlayer coupling on the electronic and vibrational properties of
recently fabricated WS₂/MoS₂ heterostructure are discussed.