Fundamentals of Quantum Chemistry Molecular Spectroscopy and Modern Electronic Structure Computations

280 Pages·2001·6.02 MB·English

by  Michael Mueller

Fundamentals of
Quantum Chemistry
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Fundamentals of
Quantum Chemistry
Molecular Spectroscopy
and Modern Electronic
Structure Computations
Michael Mueller
Rose-Hullman Institute of Technology
Terre Haute, Indiana
KLUWER ACADEMIC PUBLISHERS
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eBookISBN: 0-306-47566-9
Print ISBN: 0-306-46596-5
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Foreword
As quantum theory enters its second century, it is fitting to examine just
how far it has come as a tool for the chemist. Beginning with Max Planck’s
agonizing conclusion in 1900 that linked energy emission in discreet bundles
to the resultant black-body radiation curve, a body of knowledge has
developed with profound consequences in our ability to understand nature.
In the early years, quantum theory was the providence of physicists and
certain breeds of physical chemists. While physicists honed and refined the
theory and studied atoms and their component systems, physical chemists
began the foray into the study of larger, molecular systems. Quantum theory
predictions of these systems were first verified through experimental
spectroscopic studies in the electromagnetic spectrum (microwave, infrared
and ultraviolet/visible), and, later, by nuclear magnetic resonance (NMR)
spectroscopy.
Over two generations these studies were hampered by two major
drawbacks: lack of resolution of spectroscopic data, and the complexity of
calculations. This powerful theory that promised understanding of the
fundamental nature of molecules faced formidable challenges. The
following example may put things in perspective for today’s chemistry
faculty, college seniors or graduate students: As little as 40 years ago, force
field calculations on a molecule as simple as ketene was a four to five year
dissertation project. The calculations were carried out utilizing the best
mainframe computers in attempts to match fundamental frequencies to
experimental values measured with a resolution of five to ten wavenumbers
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in the low infrared region! Post World War II advances in instrumentation,
particularly the spin-offs of the National Aeronautics and Space
Administration (NASA) efforts, quickly changed the landscape of high-
resolution spectroscopic data. Laser sources and Fourier transform
spectroscopy are two notable advances, and these began to appear in
undergraduate laboratories in the mid-1980s. At that time, only chemists
with access to supercomputers were to realize the full fruits of quantum
theory. This past decade’s advent of commercially available quantum
mechanical calculation packages, which run on surprisingly sophisticated
laptop computers, provide approximation technology for all chemists.
Approximation techniques developed by the early pioneers can now be
carried out to as many iterations as necessary to produce meaningful results
for sophomore organic chemistry students, graduate students, endowed chair
professors, and pharmaceutical researchers. The impact of quantum
mechanical calculations is also being felt in certain areas of the biological
sciences, as illustrated in the results of conformational studies of biologically
active molecules. Today’s growth of quantum chemistry literature is as fast
as that of NMR studies in the 1960s.
An excellent example of the introduction of quantum chemistry
calculations in the undergraduate curriculum is found at the author’s
institution. Sophomore organic chemistry students are introduced to the PC-
Spartan+® program to calculate the lowest energy of possible structures.
The same program is utilized in physical chemistry to compute the potential
energy surface of the reaction coordinate in simple reactions. Biochemistry
students take advantage of calculations to elucidate the pathways to creation
of designer drugs. This hands-on approach to quantum chemistry
calculations is not unique to that institution. However, the flavor of the
department’s philosophy ties in quite nicely with the tone of this textbook
that is pitched at just the proper level, advanced undergraduates and first
year graduate students.
Farrell Brown
Professor Emeritus of Chemistry
Clemson University
Preface
This text is designed as a practical introduction to quantum chemistry for
undergraduate and graduate students. The text requires a student to have
completed a year of calculus, a physics course in mechanics, and a minimum
of a year of chemistry. Since the text does not require an extensive
background in chemistry, it is applicable to a wide variety of students with
the aforementioned background; however, the primary target of this text is
for undergraduate chemistry majors.
The text provides students with a strong foundation in the principles,
formulations, and applications of quantum mechanics in chemistry. For
some students, this is a terminal course in quantum chemistry providing
them with a basic introduction to quantum theory and problem solving
techniques along with the skills to do electronic structure calculations - an
application that is becoming increasingly more prevalent in all disciplines of
chemistry. For students who will take more advanced courses in quantum
chemistry in either their undergraduate or graduate program, this text will
provide a solid foundation that they can build further knowledge from.
Early in the text, the fundamentals of quantum mechanics are established.
This is done in a way so that students see the relevance of quantum
mechanics to chemistry throughout the development of quantum theory
through special boxes entitled Chemical Connection. The questions in these
boxes provide an excellent basis for discussion in or out of the classroom
while providing the student with insight as to how these concepts will be
used later in the text when chemical models are actually developed.
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Students are also guided into thinking “quantum mechanically” early in
the text through conceptual questions in boxes entitled Points of Further
Understanding. Like the questions in the Chemical Connection boxes, these
questions provide an excellent basis for discussion in or out of the
classroom. These questions move students from just focusing on the
rigorous mathematical derivations and help them begin to visualize the
implications of quantum mechanics.
Rotational and vibrational spectroscopy of molecules is discussed in the
text as early as possible to provide an application of quantum mechanics to
chemistry using model problems developed previously. Spectroscopy
provides for a means of demonstrating how quantum mechanics can be used
to explain and predict experimental observation.
The last chapter of the text focuses on the understanding and the
approach to doing modern day electronic structure computations of
molecules. These types of computations have become invaluable tools in
modern theoretical and experimental chemical research. The computational
methods are discussed along with the results compared to experiment when
possible to aide in making sound decisions as to what type of Hamiltonian
and basis set that should be used, and it provides a basis for using
computational strategies based on desired reliability to make computations
as efficient as possible.
There are many people to thank in the development of this text, far too
many to list individually here. A special thanks goes out to the students over
the years who have helped shape the approach used in this text based on
what has helped them learn and develop interest in the subject.
Terre Haute, IN Michael R. Mueller
Acknowledgments
Farrell B. Brown Clemson University
Rita K. Hessley University of Cleveland
College ofApplied Science
Daniel L. Morris, Jr. Rose-Hulman Institute of Technology
Gerome F. Wagner Rose-HulmanInstitute of Technology
The permission of the copyright holder, Prentice-Hall, to reproduce Figure
7-1 is gratefully acknowledged.
The permission of the copyright holder, Wavefunction, Inc., to reproduce the
data on molecular electronic structure computations in Chapter 9 is
gratefully acknowledged.
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