Density functional theory study of inter-layer coupling in bulk tin selenide

Highlights: • Larger interlayer coupling of bulk SnSe than graphite, MoS₂ and black phosphorus. • Larger interlayer coupling makes it difficult for mechanical exfoliation. We study the inter-layer coupling in bulk tin selenide (SnSe) through density functional theory based calculations. Different approximations for the exchange-correlation functionals and the van der Waals interaction are employed. By performing comparison with graphite, MoS₂ and black phosphorus, we analyze the inter-layer coupling from different points of view, including the binding energy, the low frequency inter-layer optical phonons, and the inter-layer charge transfer. We find that, there is a strong charge transfer between layers of SnSe, resulting in the strongest inter-layer coupling. Moreover, the charge transfer renders the inter-layer coupling in SnSe not of van der Waals type. Mechanical exfoliation has been used to fabricate mono- or few-layer graphene, MoS₂ and black phosphorus. But, our results show that it may be difficult to apply similar technique to SnSe.