Lateral heterostructures (LH) of monolayer-multilayer regions of the same noble transition metal dichalcogenide, such as platinum diselenide (PtSe 2), are promising options for the fabrication of efficient two-dimensional field-effect transistors (FETs), by exploiting the dependence of the energy gap on the number of layers and the intrinsically high quality of the heterojunctions. Key for future progress in this direction is understanding the effects of the physics of the lateral interfaces on far-from-equilibrium transport properties. In this work, a multi-scale approach to device simulation, capable to include ab-initio modelling of the interfaces in a computationally efficient way, is presented. As an application, p-and n-type monolayer-multilayer PtSe 2 LH-FETs are investigated, considering design parameters such as channel length, number of layers and junction quality. The simulations suggest that such transistors can …