  This review article provides a bird's-eye view of what first-principles based
methods can contribute to next-generation device design and simulation. After a
brief overview of methods and capabilities in the area, we focus on published
work by our group since 2015 and current work on $\textrm{CrI}_3$. We introduce
both single- and dual-gate models in the framework of density functional theory
and the constrained random phase approximation in estimating the Hubbard $U$
for 2D systems vs. their 3D counterparts. A wide range of systems, including
graphene-based heterogeneous systems, transition metal dichalcogenides, and
topological insulators, and a rich array of physical phenomena, including the
macroscopic origin of polarization, field effects on magnetic order, interface
state resonance induced peak in transmission coefficients, spin filtration,
etc., are covered. For $\textrm{CrI}_3$ we present our new results on bilayer
systems such as the interplay between stacking and magnetic order, pressure
dependence, and electric field induced magnetic phase transitions. We find that
a bare bilayer $\textrm{CrI}_3$, graphene$\,|\,$bilayer
$\textrm{CrI}_3\,|\,$graphene, $h$-BN$\,|\,$bilayer $\textrm{CrI}_3\,|\,h$-BN,
and $h$-BN$\,|\,$bilayer $\textrm{CrI}_3\,|\,$graphene all have a different
response at high field, while small field the difference is small except for
graphene$\,|\,$bilayer $\textrm{CrI}_3\,|\,$graphene. We conclude with
discussion of some ongoing work and work planned in the near future, with the
inclusion of further method development and applications.
