Resumen
A comparative study between two different techniques to evaluate minimum energy paths has been carried out using three simple but representative reactions. Minimum energy paths obtained from a first derivative methodology (CARTE suit program) are similar to those found with an intrinsic reaction coordinate (IRC) methodology starting from geometries characterized by a second derivative methodology. The activation energies obtained from an extrapolated curve of the first derivative minimum reaction paths showed relative errors < 5%with respect to the calculated by second derivative technique (Hessian matrix). Different optimization cycles and image numbers were used in the first derivative methodology to explore how these affect the minimum energy paths. For all the reactions studied, 25 optimization cycles were sufficient to reach a converged minimum reaction path and it was checked that in general, the use of 8 or 16 image numbers do not affect the minimum energy path behavior. We have showed how activation energies obtained from a first derivative Hamilton-Jacobi minimum energy path by a simple interpolation of an adjusted curve are in good agreement with the calculated from a second derivative methodology.

Resumen
Un estudio teórico comparativo de la absorción de NO sobre modelos de zeolites FeO-ZSM5 fue llevado a cabo usando un método parametrito de química cuantica para catálisis (CATIVIC) con cúmulos de 19, 46, 123 y 327 átomos. Los resultados muestran que el tamaño del cúmulo modelo es fundamental importancia para el modelaje de la absorción catalítica de NO. Existe una notable fortaleza del enlace Fe-N y una significativa transferencia electrónica desde los alrededores del sitio de absorción al átomo de hierro cuando el tamaño del cúmulo aumenta.