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Strain Engineering of 2D-C3N5 Monolayer and its Application in Overall Water-Splitting: A Hybrid Density Functional Study

The recent experimental synthesis of 2D graphitic C3N5 has attracted lot of interests in its electronic and optical properties and its comparison with other graphitic C3N4 and C3N3. To this end, we performed DFT calculations using more accurate HSE06 functional and estimated the corresponding electronic properties. From a comparative study of the band structures of C3N3, C3N4, and C3N5, we found that, the electronic band-gap decreases as 3.24 eV (C3N3) > 2.81 eV (C3N4) > 2.19 eV (C3N5) with increase in the number of nitrogen atoms in the unit cell of these graphitic carbon nitrides. Further, the strain dependency of the band structure of 2D g-C3N5 under uniaxial and biaxial strain is performed using the same HSE- 06 functional. We found a systematic decrease of band-gap as strain increases. Out of the two types of strain, the biaxial strain has been found to be more efficient in modulating the band-gap. The effect of strain on the structure is also explored by analyzing the bond lengths and bond-angles as well as the charge density plots. Furthermore, we found that at a biaxial strain of 20% strain an interesting structural rearrangement occurs in 2D g-C3N5, which reults in a finite magnetic moment arising from the loss of spin-degeneracy of electronic levels. Finally, by studying the evolution of band-gap, band-alignments and optical absorption as a function of strain we are able to predict that biaxially compressed C3N5 with strain in the range 12-14% can be a promising photocatalyst in overall water-splitting with an excellent optical absorption in the visible light spectrum.