The text of the Video:
Jens Peder Dahl, © ,
On my Interaction with Carl Ballhausen.
On my Interaction with Carl Ballhausen
Jens Peder Dahl , May 2002
Technical University of Denmark, Copenhagen, DK
My principal scientific interaction with
Carl Ballhausen runs through the years 1959 to 1972.
It began when Ballhausen, in the summer of 1959, came back
to Denmark from the United States, to take over the chair of
physical chemistry at the
University of Copenhagen. I had been
enrolled as a Ph.D. student in physical chemistry the same year
and was given the opportunity to attend
summer school in quantum chemistry in Sweden.
The summer school consisted of a basic part and an advanced
part, and in connection with the advanced part several prominent
quantum chemists came by and gave talks, among them the
young Professor Ballhausen. He gave a lively and very interesting
talk on ligand-field theory, spiced with the kind of distinctive
remarks which turned out to be so characteristic for him.
I had written a letter to Ballhausen from Sweden, asking him
to become my Ph.D. supervisor. Now I met him. He accepted
and very quickly found the ideal problem for me. Examine and
describe the electronic structure of the ferrocene molecule, he
said. This molecule was the prototype of a new class of
compounds known as sandwich compounds, because they were built
of two aromatic rings with a metal atom sandwiched between
them, in this case an iron atom.
During my Ph.D. project, Ballhausen gave me all the support
he could. He placed a modern electric calculator at my disposal,
he discussed with me whenever I wanted to, and during his
contact with professor Charles Coulson
in Qxford he provided a
set of very valuable integrals, worked out by Michael Barnett,
which I needed for the evaluation of my two-electron integrals.
I extended the tables as needed and succeeded in finishing what
became the first semiquantitative calculation on the ferrocene
Having acquired my Ph.D. degree I had to serve for two years
in the Danish Navy. However, I kept up the contact with
Ballhausen during this period, and he arranged that I could
afterwards spend some time with professor
John C. Slater at MIT.
The period was a suceessful one, lasting for a year and a half.
I turned back to Denmark in the summer of 1964 and gladly
accepted a position as lecturer in Ballhausen's Department.
The department had now developed into an international
center in theoretical inorganic chemistry. A large number of
postdocs and more senior visitors from the United States and
elsewhere had contributed to this. Ballhausen had published
his classic book on ligand field theory, and together with
postdoc Harry B. Gray
he had published a textbook on molecular
orbital theory, in which they developed the so-called extended
Wolfsberg-Helmholz method, a semiempirical theory that was
now being applied to many inorganic complexes. I participated
in a number of these calculations, in collaboration with several
The Wolfsberg-Helmholz method was, however, not a
sufficiently detailed theory. It was, in particular, unable to treat the
electron-electron interaction properly. We therefore gradually
abandoned it and developed more exact Hartree-Fock theories
that we applied to a number of inorganic complexes, in
collaboration with visitors and Danish students and postdocs,
In 1972, I left Ballhausen's Department of Physical Chemistry
to become a professor at the Technical University of
Denmark. Here, we made many electronic structure investigations
during the following years. But the years 1959-1972 were for
me the pioneering molecular orbital years. I am very grateful
to Carl Ballhausen for having given me the opportunity to work
with him during this fruitful period, and for the way he always
treated me as an equal and a friend.
Ballhausen has often emphasized that chemistry is an
experimental science. In accordance with this, he also set up
experimental work in spectroscopy and X-ray crystallography. Good
work was done in these fields as well, but it was theory that had
Bahlhausen's heart, and it is his theoretical works and theoretical
discussions that has bestowed upon him the high reputation
he has always enjoyed.
Last updated : March 21, 2003 - 18:16 CET