Final Activity Report Summary - QMPROC4CATALYSTDSIGN (Study of catalytic reactions mechanism and developement of systematic computational procedures for de-novo design of new catalysts ...) Traditionally, the idea that citizens have about chemical research is the work performed by people wearing white coats and making experiments behind very expensive and complicated instruments; many people will be surprised that chemistry can be done in a desk behind something as familiar as the screen of a computer. Nevertheless, computers play an important and fundamental role in chemical research. A usual definition of chemistry is 'the science fields dedicated to the study of the changes of the matter'. Therefore, the key difference between chemistry and other disciplines, as for example physics or biology, is that the subject of study is changing, and our primary role will be to understand these changes. Experimentally, we can measure the time required for a collection of molecules to change, which usually range from years to milliseconds, depending of the nature of the change (the chemical reaction). But these are the times required for a huge collection of molecules (on the order of million of million of million of million molecules). If we were able to observe an independent molecule, we will realize that during these milliseconds (or years), this single molecule remains unaltered most of the time, until, eventually, it suffers a sudden and instantaneous change. This change is so fast that it is completed in an infinitesimal fraction of a second (a hundredth of a millionth of a millionth). But what happened during this change defines the future of the molecule, whether, for example, it is transformed into a useful drug or a poison. Only the knowledge of what happened individually to each molecule is fundamental in the design of the conditions on which the changes can lead to new useful molecules. Traditionally, chemists have used the information of what happened on the macroscopic scale to infer what happens in the microscopic level. The macroscopic observation on a collection of molecules is the result of the statistics in the sudden changes of individual (microscopic) molecules, and this connection between the two allow chemists (wearing white coats and using expensive instruments) to extract some microscopic information from macroscopic observations. This approach has some limitations, and it will be extremely more useful to observe directly the changes on individual atoms and molecules. Nevertheless, this observation is not possible: the molecules are too small and the changes too fast to be measured by conventional methods, no matter how expensive and complicated is the instrument that the white coat chemist is using. A possible solution is to simulate the behaviour of the molecules. The physicists discovered, during the last century, the laws that the molecules obey during these changes. These laws are expressed in terms of very complicated equations that can be solved with the appropriate approximations and the aid of computers. During the last 19 months, thanks to the intra-European Marie Curie fellowship, we have the opportunity of studying these chemical reactions at this microscopic level. The conclusions that we obtained are very useful for the design of new procedures to perform these changes that might be useful in the preparation of compounds of interest.