  Perhaps because of the popularity that trajectory-based methodologies have
always had in Chemistry and the important role they have played, Bohmian
mechanics has been increasingly accepted within this community, particularly in
those areas of the theoretical chemistry based on quantum mechanics, e.g.,
quantum chemistry, chemical physics, or physical chemistry. From a historical
perspective, this evolution is remarkably interesting, particularly when the
scarce applications of Madelung's former hydrodynamical formulation, dating
back to the late 1960s and the 1970s, are compared with the many different
applications available at present. As also happens with classical
methodologies, Bohmian trajectories are essentially used to described and
analyze the evolution of chemical systems, to design and implement new
computational propagation techniques, or a combination of both. In the first
case, Bohmian trajectories have the advantage that they avoid invoking typical
quantum-classical correspondence to interpret the corresponding phenomenon or
process, while in the second case quantum-mechanical effects appear by
themselves, without the necessity to include artificially quantization
conditions. Rather than providing an exhaustive revision and analysis of all
these applications (excellent monographs on the issue are available in the
literature for the interested reader, which can be consulted in the
bibliography here supplied), this Chapter has been prepared in a way that it
may serve the reader to acquire a general view (or impression) on how Bohmian
mechanics has permeated the different traditional levels or pathways to
approach molecular systems in Chemistry: electronic structure, molecular
dynamics and statistical mechanics. This is done with the aid of some
illustrative examples -- theoretical developments in some cases and numerical
simulations in other cases.
