It is shown analytically and numerically that the finite-temperature many-body perturbation theory in grand canonical ensemble has zero radius of convergence at temperature when energy ordering or degree degeneracy for ground state changes with strength. When reference partially fully lifted first-order Hirschfelder-Certain degenerate theory, potential internal diverge as $T \to 0$. Contrary to...

Chalcogenide perovskites have emerged as non-toxic and stable photovoltaic materials, acting an alternative to lead halide hybrid having similar optoelectronic properties. In the present work, we report electronic optical properties of chalcogenide AZrS$_3$ (A=Ca, Sr, Ba) by using density functional theory (DFT) many-body perturbation (MBPT viz. G$_0$W$_0$ BSE). This study includes excitonic an...