  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.
