In the early 1930s, Pauling was publishing an average of one significant piece of
work every five weeks, most of it on the chemical bond or new molecular structures.
By the end of this period he had moved almost entirely away from wrestling with the
wave equation. "About 1933 or 1934 I gave up on the idea of myself making very complicated
quantum-mechanical calculations about molecular structure," he said. "I made a lot
of simple quantum-mechanical calculations and drew conclusions, and realized that
if you could ever make really accurate quantum-mechanical calculations you wouldn't
learn anything from them because they would just agree with the experiment."
He had developed his own "semiempirical" style, combining a broad application of Schrödinger’s
wave mechanics with model building and structural data from X-ray crystallography,
then matching his results with other laboratory data from across the field of chemistry.
It was a very fruitful approach. Through the early 1930s he racked up success after
success until, by 1935, he wrote, "I felt that I had an essentially complete understanding
of the nature of the chemical bond."
Slowly, his new vision of chemistry began to be accepted by other chemists. Pauling
was a persuasive salesman as well as a good researcher. He forwarded his concepts
in a flood of articles, appearances and letters. He forwarded his vision to a generation
of chemistry students who took his classes at Caltech. He used his skill as a public
speaker, his ability to communicate in the language of chemists, his eagerness to
travel widely, and his courage (some would say rashness) to publish theoretical insights
without a rigorous grounding in hard mathematics.
But one reason stood out above all: his optimism. In 1935, two observers describing
the recent advances in quantum chemistry for the Review of Modern Physics could have
had Pauling in mind when they wrote, "To be satisfied, one must adopt the mental attitude
and procedure of an optimist rather than a pessimist. The latter demands a rigorous
postulational theory, and calculations devoid of questionable approximation or of
empirical appeals to known facts. The optimist, on the other hand, is satisfied with
the approximate solutions of the wave equation. . . He appeals freely to experiment
to determine constants, the direct calculation of which would be too difficult. The
pessimist, on the other hand, is eternally worried because the omitted terms in the
approximation are usually rather large, so that any pretense of rigor should be lacking.
The optimist replies that the approximate calculations do, nevertheless, give one
an excellent 'steer' and a very good idea of 'how things go,' permitting the systematization
and understanding of what could otherwise be a maze of experimental data codified
by purely empirical valence rules."