Transition State Calculations in Gaussian: Berny, QST2, and QST3 Methods

Transition state (TS) calculations in Gaussian involve the use of various methods, such as the Berny optimization, QST2, and QST3 methods.<br /><br />The Berny optimization method is a powerful optimization technique that can be used to locate the transition state of a chemical reaction. It is based on the use of a modified version of the steepest descent algorithm and a modified version of the conjugate gradient algorithm.<br /><br />The QST2 method is a second-order quantum mechanics-based method that can be used to calculate the transition state of a chemical reaction. It is based on the use of a quadratic approximation to the potential energy surface around the transition state.<br /><br />The QST3 method is a third-order quantum mechanics-based method that can be used to calculate the transition state of a chemical reaction. It is based on the use of a cubic approximation to the potential energy surface around the transition state.<br /><br />In Gaussian, these methods can be specified by inputting the appropriate keywords and options in the input file before running the calculation.