 Given the above pre-requisites, a local optimization algorithm can then move "uphill" along the eigenvector with the most negative eigenvalue and "downhill" along all other degrees of freedom, using something similar to a quasi-Newton method.The dimer method can be used to find possible transition states without knowledge of the final structure or to refine a good guess of a transition structure.The “dimer” is formed by two images very close to each other on the PES.