IRC Calculation in Gaussian

IRC (Intrinsic Reaction Coordinate) calculation in Gaussian is used to determine the minimum energy pathway for a chemical reaction. It is performed using the "IRC" keyword in the Gaussian input file. The calculation is based on the principle of the transition state theory, which states that the rate of a chemical reaction is determined by the energy of the transition state or the highest energy point on the reaction pathway. The IRC calculation calculates the energy of the transition state and the corresponding reaction coordinates, which can be used to predict the rate and mechanism of the reaction. It is a powerful tool for understanding and predicting chemical reactions.