Living Reference Work Entry

Encyclopedia of Geochemistry

Part of the series Encyclopedia of Earth Sciences Series pp 1-6

Date: Latest Version

Ab Initio Calculations

  • David A. DixonAffiliated withDepartment of Chemistry, The University of Alabama Email author 


Molecular orbital theory is an approach to solving the Schrödinger equation for the motion of electrons in molecules (as well as atoms). Such calculations are known as ab initio (from first principles) electronic structure calculations. The molecular orbitals are usually expressed as sums of atomic orbitals, and the rules of quantum mechanics including the Pauli exclusion principle are followed. The use of molecular orbital theory ranges from qualitative where it is used to provide a description of the electron occupancy in a molecule to explain experimental results from photoelectron spectroscopy and electronic spectroscopy to extremely quantitative with a focus on precise predictions of molecular energetics and spectroscopic parameters.


Molecules contain electrons which have a low enough mass that the laws of quantum mechanics must be used to describe t ...

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