Electronic, and Optical Properties of Small Clusters of Methylammonium Tin Bromide (CH₃NH₃SnBr₃)

In this work, we studied the ground-state optimized geometry of CH₃NH₃SnBr₃ monomer, dimer, trimer, and tetramer using ab initio quantum mechanical calculations. HOMO-LUMO (∆E_L-H) gap was studied and found to be  redshifted with increasing size of (CH₃NH₃SnBr₃)_n from n =1 to 4. Optical gap  and Maximum Absorption wavelength, λ_max, were calculated. The values of (∆E_L-H)  and Optical gap for CH₃NH₃SnBr₃ clusters were approximated to be 3.622 and 3.091 electron volts respectively. Major electronic transitions observed from vertical excitation calculations show that the transitions occur from ground state to first excited state due to the excitation of one electron mainly from HOMO to LUMO. The (∆E_L-H)  value of (CH₃NH₃SnBr₃)_n clusters approximated using density of states is 2.19eV, which is close to the experimentally reported optical gap of 2.15eV. Contribution of individual atomic units to frontier orbitals was studied.