Today, quantum-chemical studies of the mechanism of electron transfer in molten salts based on a direct calculation of the transition state are faced with practically insurmountable computational difficulties. As our experience shows, model systems assigned to investigate the mechanism of charge transfer should include, in addition to the electroactive complex, two more of its coordination spheres. For electrolytes based on alkaline earth metal halides, this can be, for example, MTiF6+12MX2 type systems (M – Mg, Ca, Sr, Ba; X – F, Cl). The search for a transition state by standard methods will require enormous computer time and is almost unrealistic. In this paper, we proposed another approach, which is based on the analysis of frontier molecular orbitals (FMO) under various deformations of the initial structure.The aim of this work was the using of the method of frontier molecular orbitals to study the mechanism of the electron transfer in the CaTiF6+12CaCl2 model system.The geometry optimization of structures was performed with the Firefly program package, partially based on the source code of the GAMESS(US) program, by the density functional theory DFT/UHF method with the use of the B3LYP hybrid functional. For the F and Cl atoms quasi-relativistic basis set Stuttgart RLC ECP was used; for Ti and Ca – Stuttgart RSC 1997 ECP basis set.In this work, we were interested in the state of the complex TiF6 2- near the cathode surface. For this reason, on one side of the model system, a flat boundary layer consisting of 12-15 chlorine and calcium ions was formed. The titanium complex is in contact with one of the calcium cations belonging to the boundary layer, because our previous studies indicate the bridge nature of electron transfer to the TiF6 2- complex. Note that adding of carbon cluster to the main system CaTiF6+12CaCl2 would require a drastic increase of the computation time. However, for qualitative conclusions, it is enough to analyze the CaTiF6+12CaCl2 system.Based on the experimental data and the quantum-chemical analysis of FMO in the CaTiF6 + 12CaCl2 system, a mechanism for the charge transfer was proposed. The geometric structure of the transition state was shown to be not intermediate between the initial and final states of the system. As a result, it was found that the structure of this state is much less ordered than the initial structures of the boundary layer. The high efficiency of FMO method allows recommending this method as the instrument for testing hypotheses on the mechanism of electron transfer in molten salts.