Analysing the most probable reaction pathway from the reactant to the product is one of the central tasks of theoretical chemistry, in which Transition States (TS) are located and the barrier heights can be calculated by finding the energy difference between the TS and the reactants to analyse the feasibility of the reaction. Nevertheless, locating the TS is not trivial and is usually more challenging than locating the energy minima of stable reactants and products. A feasible approach to achieving this is to perform single-point TS optimisations based on an initial guess of the TS, then run the IRC calculation using the converged structure to find out the transition pathway. Unfortunately, due to the possible existence of low-frequency modes that affect the quality of the Hessian matrix, single-point calculations might fail to converge properly.