The nature of the lead-iodine bond in PbI2: A case study for the modelling of lead halide perovskites

[Display omitted] •Different Hamiltonian, basis sets and DFT functionals were compared.•Inclusion of the spin orbit coupling and Hartree Fock exchange is essential.•The PbI bond has a partial covalent character.•PbI2 and MAPbI3 solid state materials can be treated with the same theoretical approach. A detailed knowledge of the basic electronic interactions in lead halide perovskites components (PbI2 and methylammonium iodide) can possibly drive enhanced solar cell efficiency. We report an extensive investigation on the electronic structure and nature of the chemical bond in the PbI2 perovskite precursor, both in gas and solid state, together with a comparison with available experimental data, which allows to effectively calibrate the computational framework, along with gaining basic understanding on the nature of the PbI chemical bond. Inclusion of spin orbit coupling and calibrated HF exchange contribution to the DFT hybrid functional are proved essential for an accurate description of the electronic structure of both molecular and solid state PbI2. Such computational framework, calibrated on the model PbI2 system, can be directly translated to the accurate description of the electronic band structure of the prototypical methylammonium lead-iodide perovskite, setting the basis for the trustful modelling of different lead-halide perovskites.