The identification of a system of electrons and ions interacting with each other can be done by quantum mechanics and the properties of this system can be obtained from the solution of the multi-particle Schrödinger equation. The solution of Schrödinger's equations requires large computational capacity. Increasing the number of points used to describe the problem leads to high memory usage and increased computation time. Density functional theory is a very popular and versatile method used in physics, chemistry and materials science to calculate the electronic structure of materials. In this study, MoSe2 monolayer was created using this theory. The differences in the structures formed by Fe, Mn transition metals which are provided to be retained were investigated. Figure A. Stable MoSe2 monolayer Purpose: The aim of this study is to investigate the interaction of Fe, Mn atoms and FeMn atomic clusters due to the importance of MoSe2 monolayer which is a different semiconductor for transition metal. Theory and Methods: The optimization of MoSe2 monolayer by using quantum espresso 3.2 program in Linux operating system was achieved and the changes in the structures formed as a result of the interaction with Fe-Mn atoms used in nanoelectronic applications and catalysts were shown. In addition, the interaction of MoSe2 monolayer with transition metals was created by using package programs, energy values were calculated and their stable structures were determined. Density functional theory is used in the solution of multi-electron systems. Results: Mn, Fe, FeMn atomic and atomic clustered structures of transition metals of MoSe2 monolayer were examined by generalized gradient approach using density functional theory. The changes in the properties of the resulting stable structures were examined and the differences in the magnetic properties were shown. In addition, it was determined how stable structures determined according to their holding energies change in different atoms. Conclusion: The results of the study showed that the methods used and the potentials were appropriate when compared with similar literature studies. In addition, the results showed that the theory used was suitable for the semiconductor and transition metals studied.