Page 15 - Strategies and Applications in Quantum Chemistry From Molecular Astrophysics to Molecular Engineer

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In the few years which followed his first steps in the field he succeeded in investigating by
the relatively simple Hückel approximation a large number of new and fascinating problems
in organic chemistry of conjugated systems. This involved, in particular an extremely vast
exploration of non-aromatic benzenoid compounds, starting from the small fulvene and
azulene up to rather very complicated thermochromic ethylenes, a study which led to the
discovery of a number of unpredicted and surprising properties, in particular in the field of
dipole moments and ultra-violet spectra, which contradicted a number of rules "established"
by the resonance theory. A special mention must be given to his contribution to the
theoretical exploration of the diamagnetic properties of polycyclic hydrocarbons and of the
electronic structure of free radicals and biradicals. This very prolific activity was carried out
in the early fifties.

Parallel to this use of relatively simple approximations of the molecular orbital theory to the
study of complex molecules Berthier has investigated the possible utilization of more
refined molecular orbital procedures in the study of necessarily smaller molecules. We owe
him the first application of the SCF method to the study of fulvene and azulene and also a
pioneering extension, presented in 1953, of the SCF method to the study of molecules with
incomplete electronic shells.

This was altogether a most important period in the history of quantum chemistry in France,
when slowly but surely the electrons gained the right of citizenship in chemistry. Berthier is
largely responsible for this success both through his scientific contributions and through the
influence which he has exerted on an number of young students and the enthusiasm which
he has distilled in them. He had the chance of becoming a good friend of another of our
research collaborators in these early years, Madame Serre who was to become later the
Director of the Ecole Normale Supérieure de Jeunes Filles. Berthier used to divide his time
between our laboratory and that of Madame Serre; the latter enabled him to have the greatest
number of female students among all the quantum chemists in the world. This is, may be,
why he remained a bachelor.
We are referring here only to the early years of Berthier's activity in the field of quantum
chemical theory. These were the decisive ones and from some point of view the most
difficult but also exciting ones. Needless to say, everybody knows it, that he has continued
since and continues still, to contribute in a most efficient way to the development and
propagation of quantum chemistry and, at this time, not only in France but on the world
scene.

A. Pullman B. Pullman