Constrained optimization procedure for finding transition states and reaction pathways in the framework of gaussian based density functional method: the case of isomerization reactions

Abstract

Reaction profiles and transition state structures (TS) have been obtained with a new algorithm for finding saddle points on potential energy surfaces. Results are presented for a series of representative isomerization reactions. The algorithm is based on constrained optimization techniques and it is implemented in the LCGTO-DF (linear combination of Gaussian-type orbitals-density functional) program deMon. It can be considered as a step-by-step walking uphill process along the minimum energy path, followed by a refining procedure of TS parameters in the saddle point vicinity. The obtained transition state structures and energy barriers are similar to those determined by ab-initio methods in which electron correlation is taken into account. At present, our results for CH3NC-->CH3CN, for which the experimental barrier is known, are the most accurate theoretical determination. The coupling between the new algorithm and the LCGTO-DF method seems to be an effective tool to obtain reliable TS structures and energy barriers for complex potential energy surfaces.