12 Possible Orientations of organic Formamidinium cation and its structural analysis by First Principles calculations using Van der Waals-Density functional Theory

Stability threshold of formamidinium lead iodide determined by strain amplitudes

“…The uniaxial -δ regular behavior is obtained for the following combinations of strain paths and FA planes: The Mulliken charge (MC) population analysis for the uniaxial -δ regular at δ i = −δ max shows a high bond population in the order of −0.11e, with a bond length around 2.83 Å, both values found among H 5 -I 2 &H 4 -I 2 bonds. Meanwhile, a much smaller population is obtained in between H 3 -I 2 &H 2 -I 2 bonds (−0.04 e & 2.90 Å), which is similar to the charge distribution found at the FAPbI 3 ground state [16]. At the opposite strain boundary δ i = δ max , the MC bond population shows similar results as the former case (−0.11e for both H 5 -I 2 &H 4 -I 2 and −0.02e for both H 3 -I 2 &H 2 -I 2 ), however, a slight exchange in the bond length is observed, since the values are now distributed as: 2.87 and 2.84 Å, for both H 5 -I 2 &H 4 -I 2 and H 3 -I 2 &H 2 -I 2 , respectively.…”

“…The numerical EC values show that both uniaxial -δ regular and planar -δ regular behaviors are attained at: c 33 , c 66 , and c 12 , each of them with averages around 32.77, 1.78, and 8.09 GPa, for the [XY] FA cation plane, respectively. On the other hand, for non-regular cases, there is an equivalence in the elastic response in between the FA clockwise orientation at 12:00 and 06:00, which is also present at 03:00 and 09:00, for all c ij values, as it was discussed for the optimized lattice parameters (table 1 [16],). It is prominent to mention that all deformations below an amplitude equal to 0.02 generate positive elastic constants fulfilling the stability criteria for orthorhombic structures (table 1).…”

“…Our previous work [16] on the structural analysis of FAPbI 3 perovskite showed the equilibrium lattice parameters follow two tendencies, as a function of the clockwise rotation of the FA cation. For the first case, the length of the lattice parameter that is parallel to the N-N axis is larger and the one perpendicular diminishes its length, becoming the most compact.…”

A review on theoretical studies of structural and optoelectronic properties ofFA‐based perovskite materials with a focus onFAPbI3

“…Karthick et al rotated the FA molecule in 12 positions, finding a behavioral change in the lattice parameter. Furthermore, they indicated that electron charge density distribution between the two hydrogen atoms (H4 and H5) and iodine atom varies the volume 88 …”