||Mechanical exfoliation is the method used in isolating the first two-dimensional material, graphene, and has so far been widely applied to two-dimensional materials. Since there are many possibilities of mechanically exfoliating two-dimensional materials from known bulk materials, it is important to calculate the required energy to assess how feasible such exfoliation is. Traditionally, however, the computation of exfoliation energy required simulations of a thick-enough slab to mimic the surface of a bulk material. In this presentation, we discuss a new method of calculating exfoliation energy that is conceptually rigorous and requires a significantly less amount of computational resource [J.-H. Jung, C.-H. Park, and J. Ihm, Nano Lett. 18, 2759 (2018)].