Enormous excitonic effects in bulk, mono- and bi- layers of cuprous halides using many-body perturbation technique

Electronic band structure of cuprous and silver halides: An all-electronGWstudy

“…qualitatively wrong metallic state, which deteriorates the reliability of the predictions by practical LDA/GGA based DFT calculations. Previous work confirmed that the band gaps predicted for cuprous and silver halides by LDA/GGA are typically smaller than experimental values by 1-2 eV, 4,[24][25][26] and the problem is only partly remedied when using the hybrid functional approximation. 23,27 The many-body perturbation theory based on Green's function in the GW approximation has proven to be able to accurately predict electronic band structure of typical semiconductors, [28][29][30] and it has been applied in attempt to resolve the band-gap problem in cuprous and silver halides.…”

“…Cuprous halides are wide-gap semiconductors with large exciton binding energy, and are promising candidates for applications in optoelectronic devices. [1][2][3][4] In particular, being a native p-type semiconductor, 5 the transparent CuI film has not only been employed as a hole transport material in solar cells, [6][7][8] but also shown exceptional performance as a thermoelectric material. 9 Silver halides has been used in light conversion since mid-1800s, owing to their high photosensitivity.…”

“…17 However, despite their wide applications, a thorough theoretical understanding of fundamental properties of this class of materials is still lacking, e.g. the phase transition of CuI at high temperature, 18,19 the extraordinarily large excitonic binding energy of CuX, 4,20 and the electronic dynamics within AgX in the latent image formation. [21][22][23] Nowadays, first-principles electronic structure calculations are being practiced routinely to predict electronic and optical properties of materials.…”

“…23,27 The many-body perturbation theory based on Green's function in the GW approximation has proven to be able to accurately predict electronic band structure of typical semiconductors, [28][29][30] and it has been applied in attempt to resolve the band-gap problem in cuprous and silver halides. 4,27,[31][32][33] However, LDA/GGA-based G 0 W 0 calculations generally give underestimated band gaps for these materials. 4,[31][32][33] Particularly in CuX, the error ranges from 0.7 to 2.7 eV for the band gap at Γ, [31][32][33] with the largest error observed in CuCl.…”

“…4,27,[31][32][33] However, LDA/GGA-based G 0 W 0 calculations generally give underestimated band gaps for these materials. 4,[31][32][33] Particularly in CuX, the error ranges from 0.7 to 2.7 eV for the band gap at Γ, [31][32][33] with the largest error observed in CuCl. 32 Although it is well known that one-shot GW calculations based on LDA/GGA tend to underestimate the band gaps for semiconductors, 34,35 it is inferred by the exceptionally large error that some essential ingredients may be missing in the employed LDA/GGA-based G 0 W 0 implementation to predict accurate band gaps for the cuprous compounds.…”