Quantum chemistry



See also: theoretical chemistry.

Quantum chemistry is a branch of physical chemistry.

Quantum chemistry mathematically describes the fundamental behavior of matter at the orbital approximation) can be understood and applied in simpler terms.

In quantum mechanics (several applications in computational chemistry and quantum chemistry), the Hamiltonian, or the physical state, of a particle can be expressed as the sum of two operators, one corresponding to kinetic energy and the other to potential energy. The Hamiltonian in the Schrödinger wave equation used in quantum chemistry does not contain terms for the spin of the electron.

Solutions of the Schrödinger equation for the hydrogen atom gives the form of the wave function for carbon.

History

Main article: History of quantum mechanics

The history of quantum chemistry began essentially with the 1838 discovery of cathode rays by Max Planck that any energy radiating atomic system can theoretically be divided into a number of discrete ‘energy elements’ ε such that each of these energy elements is proportional to the frequency ν with which they each individually radiate energy, as defined by the following formula:

\epsilon = h \nu \,

where h is a numerical value called Planck’s Constant. Then, in 1905, to explain the photons (1926). In the years to follow, this theoretical basis slowly began to be applied to chemical structure, reactivity, and bonding.

Electronic structure

Main article: Computational chemistry#Electronic structure

The first step in solving a quantum chemical problem is usually solving the Schrödinger equation (or electronic molecular Hamiltonian. This is called determining the electronic structure of the molecule. It can be said that the electronic structure of a molecule or crystal implies essentially its chemical properties.

Wave model

The foundation of quantum mechanics and quantum chemistry is the wave model, in which the atom is a small, dense, positively charged wave-particle duality.

Valence bond

Main article: Valence bond theory

Although the mathematical basis of quantum chemistry had been laid by bonds.

Molecular orbital

Main article: Molecular orbital theory

An alternative approach was developed in 1929 by Friedrich Hund and post Hartree-Fock methods.

Density functional theory

Main article: Density functional theory

The computational chemistry at present.

Chemical dynamics

A further step can consist of solving the Schrödinger equation with the total Monte Carlo methods, are also possible.

Adiabatic chemical dynamics

Main article: Adiabatic formalism or Born-Oppenheimer approximation

In adiabatic dynamics, interatomic interactions are represented by single scalar potentials called Eyring in 1935 into account. These methods enable simple estimates of unimolecular reaction rates from a few characteristics of the potential surface.

Non-adiabatic chemical dynamics

Main article: Vibronic coupling

Non-adiabatic dynamics consists of taking the interaction between several coupled potential energy surface (corresponding to different electronic quantum states of the molecule). The coupling terms are called vibronic couplings. The pioneering work in this field was done by Stueckelberg, Landau, and Zener in the 1930s, in their work on what is now known as the Landau-Zener transition. Their formula allows the transition probability between two avoided crossing to be calculated.

Quantum chemistry and quantum field theory

The application of quantum field theory (QFT) to chemical systems and theories has become increasingly common in the modern physical sciences. One of the first and most fundamentally explicit appearances of this is seen in the theory of the photomagneton. In this system, quantum hydrodynamics. Field theoretic methods have also been critical in developing the ab initio Effective Hamiltonian theory of semi-empirical pi-electron methods.

See also

Further reading

  • Pauling, L. (1954). General Chemistry. Dover Publications. ISBN 0-486-65622-5. 
  • Pauling, L., and Wilson, E. B. Introduction to Quantum Mechanics with Applications to Chemistry (Dover Publications) ISBN 0-486-64871-0
  • Atkins, P.W. Physical Chemistry (Oxford University Press) ISBN 0-19-879285-9
  • McWeeny, R. Coulson's Valence (Oxford Science Publications) ISBN 0-19-855144-4
  • Landau, L.D. and Lifshitz, E.M. Quantum Mechanics:Non-relativistic Theory(Course of Theoretical Physics vol.3) (Pergamon Press)
  • Eric R. Scerri, The Periodic Table: Its Story and Its Significance, Oxford University Press, 2006. Considers the extent to which chemistry and especially the periodic system has been reduced to quantum mechanics. ISBN 0-19-530573-6

Nobel lectures by quantum chemists

  • Walter Kohn's Nobel lecture
  • Rudolph Marcus' Nobel lecture
  • Robert Mulliken's Nobel lecture
  • Linus Pauling's Nobel lecture
  • John Pople's Nobel lecture

References

  1. ^ Quantum Chemistry. The NIH Guide to Molecular Modeling. National Institutes of Health. Retrieved on 2007-09-08.
 
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