# Collaboration with professor Bhattacharya in ab initio spectroscopy of 2D materials results in the first paper in JPCC

Giant Linear and Nonlinear Excitonic Responses in an Atomically Thin Indirect Semiconductor Nitrogen Phosphide

(ACS)

Miroslav Kolos, Luigi Cigarini, Rekha Verma, František Karlický, and Sitangshu Bhattacharya

Abstract

Large linear and nonlinear optical responses can be obtained from two-dimensional semiconductors with an indirect electronic gap. Here, we demonstrate exceptionally large exciton-driven responses such as the fundamental exciton binding energy (2 eV), zero-point band-gap re normalization (200 meV), and nonlinear second and third harmonic coefficients (800 pm/V and 1.4×10−18m^{2}/V^{2}, respectively) from an atomically thin binary group-V nitrogen phosphide (NP) semiconductor. The influence of lattice vibrations on the absorption spectra unfolds strong electronic couplings to both LA and ZO-TO phonon modes. All the linear process analyses were computed using a fully *ab initio*-based G_{0}W_{0}+ Bethe−Salpeter equation approach that also includes the electron−phonon self-energies. Then on linear processes were instead obtained using a real-time *ab initio* process flow after creating a coupling between the time-dependent external electric field and the correlated electrons within the modern theory of polarization and the same electron−hole interaction level.