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Quantum chemistry is the application of quantum mechanics to chemical systems. In experimental physics, quantum chemists rely on spectroscopy. In theoretical physics, however, quantum chemists seek to calculate the predictions of quantum theory. Atoms and molecules here, can only have discrete energy.
Ground states of individual atoms and molecules are studied. The excited and transition states that exist in chemical reactions are also studied.
Quantum chemists use quantum mechanical principles. They deal with time dependent problems. Many times it is assumed that the nuclei are at rest.
Major goals of quantum chemistry:
Increasing the accuracy of results for small molecular systems.
Increasing the size of large molecules that can be processed.
Some view the birth of quantum chemistry as the discovery of the Schrodinger equation. This equation had applications to the hydrogen atom in 1926. This laid the mathematical basis for quantum chemistry. In fact, solving the Schrodinger equation is the first step in many quantum chemical problems. However, in relativistic quantum chemistry, the Dirac equation can be used. This is how the electronic structure of the molecule is determined.
Walter Heitler
Fritz London
Walter Heitler and Fritz London, proposed an article in 1927.
This is recognized as a milestone in the history of quantum chemistry.
This was an application of quantum mechanics to the diatomic hydrogen molecule (the phenomenon of the chemical bond.) Heitler showed how to use the Schrodinger wave equation to show how two hydrogen atom wave functions join together. Him and London worked out the details of the theory.
Max Born
J. Robert Oppenheimer
Much progress was also made by Max Born, who was instrumental in the development of quantum mechanics, and J. Robert Oppenheimer, who made important contributions to quantum mechanics and quantum field theory.
Born won the 1954 Nobel Prize in Physics for his fundamental research in quantum mechanics and for his statistical interpretation of the wave function.
Oppenheimer made the first prediction of quantum tunneling.
Michael Faraday
In 1838, Michael Faraday discovered Cathode rays.
Cathode rays are streams of electrons. They are observed in vacuum tubes.
Faraday applied a high voltage between two metal electrodes. These were at either end of a glass tube. This glass tube has been partially evacuated of air. Faraday noticed a strange light arc. This arc began at the cathode or positive electrode and ended at the anode or negative electrode.
Gustav Kirchoff
Gustav Kirchoff, in 1859, contributed to the fundamental understanding of the emission of black-body radiation by heated objects.
He actually coined the term "black-body radiation." He did this in 1862.
Ludwig Boltzmann
Max Planck
Ludwig Boltzmann can be considered among the fathers of quantum mechanics for his 1877 proposal that the energy states of a physical system can be discrete. Indeed, the energy levels of a physical system could be discrete.
Max Planck, in 1900, gives his quantum hypothesis that any energy radiating atomic system can be theoretically divided into a number of discrete energy elements. Each of these energy elements is proportional to the frequency.
Albert Einstein
Albert Einstein, in 1905, attempts to explain the photoelectric effect. Shining light on certain materials can eject electrons from that material.
Einstein will propose, building on Planck's work, that light consists of individual particles. These later came to be known as photons.
Linus Pauling
Linus Pauling, is considered one of the founders of quantum chemistry. This was probably one of the greatest contributions to the field. Pauling's focus was to research and focus on how the chemical properties of atoms are related to the structure of atoms of which they are composed. Pauling was a pioneer in the application of the quantum theory to the molecule.
Pauling developed two concepts in valence bond theory:
Resonance (1928) - Pauling used this to explain the partial valence of molecules.
Orbital hybridization (1930) - Pauling developed this theory to explain simple molecules such as methane using atomic orbitals.
Attention is given to the pairwise interaction between atoms. It focuses on how the atomic orbitals can combine to give individual chemical bonds when a molecule is formed.
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