The computational calculations nowadays do not act as a support element for supporting experimental results. Now we have taken more ambitious roles, going forward and saving time and money to the experimental sector. Thus we will tackle existing unexplained effects in olefin metathesis, including no stability, no or low activity, deactivation of the catalysts. By means of DFT, the design of more active catalysts will render the method of wider use as a tool for molecular assembly, rendering syntheses simpler and faster by reducing the number of required reactions to obtain the desired molecule, thus a reduction of the amount of waste produced too.The science outlined impacts the pharmaceutical world in numerous ways.Several quantum mechanics studies have been performed to rationalize the mechanism of olefin metathesis promoted by Ru-based catalysts. However, with the single exceptions of an old study on an oversimplified system, and 2-3 projects, all the computational results published to date have been obtained with static techniques. The dynamic studies are able to escape from the limits of our understanding of this important reaction.Half of the project is focused on an ab initio molecular dynamics simulation of Ru-catalyzed olefin metathesis. Taking advantage of the state-of-the-art ab initio molecular dynamics simulation CP2K package the dynamic characterization of the metathesis reaction pathway from reactants to products will be investigated. Free energy surfaces connecting the reactants to the Ru-metallacyclobutane key intermediate and finally to the products will be reconstructed from the simulations. Furthermore, simulations will be also performed to clarify the isomerization pathways that connect different reaction pathways corresponding to different geometric isomers of the catalyst, and usually labeled as side and bottom reaction pathways. From molecular dynamics, metadynamics and transition path sampling will be the chosen tools.