Page 18 - Strategies and Applications in Quantum Chemistry From Molecular Astrophysics to Molecular Engineer

QUANTUM CHEMISTRY: THE NEW FRONTIERS 3

Thirty years later we may compare these indications of possible trends in the evolution of
theoretical chemistry with the present status of the discipline. The separation into three
separate disciplines has not been happened. Grace to the efforts of a small number of
persons aware that the primary objective of theoretical chemists is to interpret chemical
phenomena, and that for this interpretation the semi-quantal interpretative tools elaborated
in the preceding stage of the discipline were nothing more that imperfect, provisional
instruments, the links between the first two approaches have been reinforced. The handful
of persons I refer here - the names of whom are familiar to every theoreticians and among
whom I would here remember Berthier - took the correct position that the most efficient
way of improving interpretative tools was to work, personally or through the younger men
under their control, on both sides, in the implementation of new computational and
theoretical methodologies, and in the exploitation of these progresses for the definition and
refinement of the interpretative tools.

An analogous role has been played by other scientists in strengthening the ties between
quantum chemistry of type I (and type II) with the area corresponding to biochemistry (or
complex molecular systems in general), a task made more difficult by the explosive growth
of structural and functional information about biomolecular systems. It is worth to remark
here that such a fruitful use of quantum chemical concepts in biology has requested the
extension of the methods to approaches different from quantum molecular theory in the
strict sense introduced before. We shall comeA back to this remark later.

I think that the majority of my colleagues will agree with this statement: Coulson's worries
are not become a reality, theoretical chemistry has survived to the impact with
computerized quantum mechanics and has grown in a complex discipline, rich of different
facets, and with an increasing weight in chemistry.
It rests however that many aspects of the Coulson analysis were correct: he rightly singled
out the three most important directions of progress in theoretical chemistry (we may add
now a fourth group). There has not been a complete divorce among the three groups but a
sizeable number of scientists continues to work with enthusiasm and success (we shall
distinguish later between enthusiasm and success) on the development of formal theories
and on their translation into computational codes, without bothering much about chemistry,
while another active group produces model about complex structures and functionalities in
large complex systems, without paying much attention to the congruence with the basic
paradigms of the discipline which remain those of quantum mechanics.

As anticipated before there is now another group, called in the following pages group III,
those of persons making computations on chemical systems (and on chemical phenomena)
with the goal of getting specific information about structure, energetics, observables, as
derived from the calculations, without any methodical attempt of "understanding" the
phenomenon
The presence of these strong differences in the community of theoretical chemists is mainly
due to the explosive growth of the discipline. Theoretical chemistry has kept the pace with
science in general in the ever increasing rate of development, and this remark, which could
be substantiate with many indicators, like the number of journals, the number of new of
sub-disciplines, of new scientific societies, etc., points out that theoretical chemistry
enjoys good health
We have to acknowledge the situation sketched here, a discipline which has got over the
peril of complete fragmentation during a stage of sudden change, and the presence of at
least four subgroups with well differentiated interests. This will be starting point for our
attempt of indicating the most probable, and the most hoped, lines of evolution.