Quantum chemistry composite methods

<p>Quantum chemistry composite methods (also referred to as thermochemical recipes) are <a href="/facts/Computational_chemistry/KyuCgRV3">computational chemistry</a> methods that aim for high accuracy by combining the results of several calculations. They combine methods with a high level of theory and a small <a href="/facts/Basis_set_(chemistry)/rQCPt3yl">basis set</a> with methods that employ lower levels of theory with larger basis sets. They are commonly used to calculate thermodynamic quantities such as enthalpies of formation, atomization energies, ionization energies and electron affinities. They aim for chemical accuracy which is usually defined as within 1 kcal/mol of the experimental value. The first systematic model chemistry of this type with broad applicability was called Gaussian-1 (G1) introduced by <a href="/facts/John_Pople/1UmPknsL">John Pople</a>. This was quickly replaced by the Gaussian-2 (G2) which has been used extensively. The Gaussian-3 (G3) was introduced later.
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Quantum chemistry composite methods open-in-new

Quantum chemistry composite methods