Metal halide perovskites (MHPs) for perovskite solar cells (PSCs) have gained great attention in just few years due to their rapid increase of photoconversion records of efficiency.  In addition, MHPs exhibit a competitive fabrication cost together with a simple route to synthetize. Due to these facts, PSCs are recognized by scientists as a promising technology with enormous potential in the energy market. However, it is well known that many factors cause the degradation of PSCs, thus, industrial applications are critically hampered by instability issues.[1]

Nowadays, experimental and theoretical researchers are investigating many possible alternatives to increase the stability of PSCs. In this context, computational techniques are being extremely useful to understand the properties of MHPs at microscopic level that cause instability of the material. Density functional theory (DFT) calculations are the key method for studying material properties, but the high computational cost limits the study to small systems and short time-scales. Classical simulations seem to be an option to overcome these limitations, but they suffer from other drawbacks such as classical simulations cannot describe electrons and chemical reactions. Therefore an intermediate approach between DFT and classical simulations is often desired. In this regard, semi-empirical Quantum Mechanics methods, such as density functional tight binding (DFTB), combine the functionalities of describing both electrons and ions. Traditional DFTB methods are based on a simplification of the Kohn-Sham DFT total energy, using pre-computed interactions of element pairs, considerably reducing the computational cost. However, this parameterization lacks of transferability and is limited to a number of elements. A new extended tight binding method called GFN1-xTB [2] has been recently developed to cover all the elements of the periodic table. This method has the advantageous of maintaining high accuracy and a limited number of parameters which can be refined for the study of a given application.

In this work, we investigate the performance of GFN1-xTB for the study of geometrical, optoelectronic, and vibrational properties of MHPs. We study organic and inorganic MHPs with formula ABX₃, with A = MA, FA, and Cs; B = Pb and Sn; X = I, Br, and Cl, being a total of 18 MHPs with cubic, tetragonal, and orthorhombic forms. We found that even further refinement of the GFN1-xTB parameters can be done to increase the accuracy of the method, the original set of parameters is adequate to study the properties of MHPs.