Dear Sai Kumar.

The concept of an activation energy spectrum (AES) has been successfully applied in modelling the kinetics of structural relaxation displayed by many physical properties of metallic glasses a combination of a constant, physically reasonable value of v0 with broad gaussian spectra of activation energies can provide a good fit to observed isothermal kinetic data.There is depending on your selection, Gaussian may use the Moller-Plesset fourth order correlation energy correction with single, double, triple and quadruple substitutions. Energetic collisions between molecules cause interatomic bonds to stretch and bend farther, temporarily weakening them so that they become more susceptible to cleavage. Distortion of the bonds can expose their associated electron clouds to interactions with other reactants that might lead to the formation of new bonds. the basic equations used to calculate thermochemical quantities in Gaussian are based on those used in standard texts. Since the vibrational partition function depends on the frequencies, you must use a structure that is either a minimum or a saddle point. For electronic contributions to the partition function, it is assumed that the first and all higher states are inaccessible at the temperature the calculation is done at. The data generated by Gaussian can be used to calculate heats and free energies of reactions as well as absolute rate information.

regards,

Prem Baboo

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiQ1KnP0t7NAhVBuo8KHWzxD5MQFgggMAA&url=http%3A%2F%2Fwww.gaussian.com%2Fg_whitepap%2Fthermo.htm&usg=AFQjCNHIlLkuP3IVMYRQR-iHiJK4tlE3KA&sig2=weAAaARzCqjiQH6w2QbgmA

Upto my understanding, u want to study the reaction in presence of some catalyst surface...r u looking for software to creat surface???? if in case you can use the same software that you used to create reactant molecules. for example, gaussview...you can create structures....but gaussian you cannot handle periodic structures.... you should search for an alternate software to run the calculations and the periodic surfaces can be created using materialstudio kind of softwaes....

if u want to sytudy the reaction over some metal clusters you can create them in gaussview and you can optimize them in gaussian. then simply you can copy the optimized structure to the reactants geometry and you can arrange them for reaction. Prem Baboo has given some good information about the theoretical study....it may help you to understand what is happening in gaussian.