Theoretical chemistry involves the use of physics
to explain or predict
chemical phenomena.
In recent years, it has consisted primarily of
quantum chemistry, i.e., the application
of
quantum mechanics to problems
in chemistry. Theoretical chemistry may be broadly divided into
electronic structure, dynamics, and statistical mechanics. In the
process of solving the problem of predicting chemical
reactivities, these may all be invoked to various
degrees. Other "miscellaneous" research areas in theoretical
chemistry include the mathematical characterization of bulk
chemistry in various phases (e.g. the study of
chemical kinetics) and the study of the
applicability of more recent math developments to the basic areas
of study (e.g. for instance the possible application of principles
of topology to the study of electronic structure.) The latter area
of theoretical chemistry is sometimes referred to as
mathematical chemistry.
Much of this may be categorized as
computational chemistry, although
computational chemistry usually refers to the application of
theoretical chemistry in an applied setting, usually with some
approximation scheme such as certain types of
post Hartree-Fock,
Density Functional Theory,
semiempirical
methods (such as
PM3) or
force field methods. Some
chemical theorists apply
statistical mechanics to provide a
bridge between the microscopic phenomena of the quantum world and
the macroscopic bulk properties of systems.
Theoretical attacks on chemical problems go
back to the earliest days, but until the formulation of the
Schrödinger equation by
the Austrian physicist Erwin
Schrödinger, the techniques available were rather crude and
speculative. Currently, much more sophisticated theoretical
approaches, based on
Quantum Field
Theory and Nonequilibrium Green Function Theory are in
vogue.
Branches of theoretical chemistry
- Quantum chemistry: The
application of quantum mechanics
to chemistry
- Computational chemistry:
The application of computer codes to
chemistry
- Molecular modelling: Methods
for modelling molecular structures without necessarily referring to
quantum mechanics. Examples are molecular docking, protein-protein docking, drug design, combinatorial chemistry.
- Molecular dynamics:
Application of classical
mechanics for simulating the movement of the nuclei of an
assembly of atoms and molecules.
- Molecular mechanics:
Modelling of the intra- and inter-molecular interaction potential energy surfaces via a sum
of interaction forces.
- Mathematical chemistry:
Discussion and prediction of the molecular structure using
mathematical methods without necessarily referring to quantum
mechanics.
- Theoretical chemical kinetics:
Theoretical study of the dynamical
systems associated to reactive chemicals and their corresponding differential equations.
- Cheminformatics (also known as
chemoinformatics): The use of computer and
informational techniques, applied to a range of problems in the
field of chemistry.
Closely related disciplines
Historically, the major field of application of theoretical
chemistry has been in the following fields of research:
- Atomic physics: The discipline
dealing with electrons and atomic nuclei.
- Molecular physics: The
discipline of the electrons surrounding the molecular nuclei and of
movement of the nuclei. This term usually refers to the study of
molecules made of a few atoms in the gas phase. But some consider
that molecular physics is also the study of bulk properties of
chemicals in terms of molecules.
- Physical chemistry and
chemical physics: Chemistry
investigated via physical methods like laser
techniques, scanning
tunneling microscope, etc. The formal distinction between both
fields is that physical chemistry is a branch of chemistry while
chemical physics is a branch of physics. In practice this
distinction is quite vague.
- Many-body theory: The
discipline studying the effects which appear in systems with large
number of constituents. It is based on quantum physics – mostly second quantization formalism – and
quantum
electrodynamics.
Hence, the theoretical chemistry discipline is sometimes seen as a
branch of those fields of research. Nevertheless, more recently,
with the rise of the
density
functional theory and other methods like
molecular mechanics, the range of
application has been extended to chemical systems which are
relevant to other fields of chemistry and physics like
biochemistry,
condensed matter physics,
nanotechnology or
molecular biology.
Bibliography
- Attila Szabo and Neil S. Ostlund, Modern Quantum Chemistry:
Introduction to Advanced Electronic Structure Theory, Dover
Publications; New Ed edition (1996) ISBN 0486691861, ISBN
978-0486691862
Quotations