Nonadiabatic transitions between electronic excited states play important roles in photochemistry and photophysics of molecular systems. One special kind of nonadiabatic transition is an internal conversion process near a conical intersections. A classic example of ultrafast internal conversion through a conical intersection is the ultrafast relaxation process from S2 to S1 of pyrazine. In this work, we introduce the properties of the conical intersection and a minimal model to describe a system with a conical intersection. By applying the parameters in pyrazine based on literatures, we can construct potential energy surfaces with a conical intersection in pyrazine. By tuning the parameters, we can find how these parameters affect the position of a conical intersection. Also, based on literatures, only a few modes contribute to this process in pyrazine. Thus, based on normal mode analysis, we can see motions of 24 normal modes and see the animation of proposed modes in literature which contribute to the process. This worksheet uses the Maple Quantum Chemistry Toolbox.