Divisions one hesitates to stress the term division

divisions (one hesitates to stress the term division) should not be a complete
outsider in any of the other three. That said, whether someone working in one of
the “conventional” fields is doing computational chemistry depends: the term could
be taken to mean calculation used to anticipate or rationalize experimental results,
to predict unrealized chemistry, or to explain (usually puzzling) experimental
results. So a kineticist might use computations to predict or explain rate constants,
or an organic chemist might use computations to predict or explain the properties of
novel organic compounds.
586 Answers

Work in one of the conventional fields is not, by tradition, regarded as com-
putational chemistry, but it can become such if the principles of computational
chemistry (such as computational characterization of putative intermediates and
transition states) are applied to a problem in the field.
Theoretical chemistry rates some special mention in this context. Nowadays this
activity tends to be quite mathematical [1], but history shows us that theoretical
chemistry need not be mathematical at all. From the first years of the crystallization
of chemistry as a subject distinct from alchemy, chemists have utilized theory, in
the sense of disciplined speculation. Nonmathematical examples are found in the
structural theory of organic chemistry [2] and in most applications of the powerful
Woodward–Hoffman orbital symmetry rules [3].
References
1. Wilson EK (1996) Chemical and Engineering News, August 19, p 35
2. (a) Nye MJ (1993) From chemical philosophy to theoretical chemistry. University of California
Press, Berkeley, CA. (b) Gould RF (ed) (1966) Kekule symposium, Advances in Chemistry
Series. American Chemical Society Publications, Washington, DC
3. Woodward RB, Hoffmann R (1970) The conservation of orbital symmetry. Verlag Chemie,
Weinheim
Chapter 1, Harder Questions, Answers
Q3
The properties of a molecule that are most frequently calculated are geometry,
energy (compared to that of other isomers), and spectra. Why is it more of a
challenge to calculate “simple” properties like melting point and density?
Hint: Is there a difference between a molecule X and the substance X?
Properties like geometry, energy, and spectra are characteristics of single mole-
cules (with the reservation that close contact with other molecules, especially
solvation or crystal packing, can affect things), while melting point and density
are bulk properties, arising from an ensemble of molecules. Clearly it should be
easier to deal with a single molecule than with the hundreds or thousands (at least)
that make up even a tiny piece of bulk matter.
Melting points have been calculated [1] extracting thermodynamic information
about the solid and liquid phases by molecular dynamics simulations [2].