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The electronic absorption spectrum is a key tool in studying electronic structure and material identification, enabling the investigation of molecular changes in chemical reactions and the dynamic behavior of molecules in excited states. Accurate calculations of the absorption spectrum require consideration of nuclear motion alongside electronic transitions, achieved by approximations that incorporate the nuclear wavefunction into electronic transitions. In this process, methods that calculate the potential energy surface of the excited state play a pivotal role. In this thesis, we employed the Adiabatic Hessian, Adiabatic Hessian After a Step, Vertical Hessian and Vertical Gradient methods....