IOP roadmap : semiempirical methods

Bannwarth, Christoph and Hourahine, Ben and Moussa, Jonathan (2024) IOP roadmap : semiempirical methods. Electronic Structure. ISSN 2516-1075 (

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Semiempirical electronic structure methods reduce the cost of solving the many-body Schr¨odinger equation by simple models and approximate solutions and mitigate the resulting errors with parameters fitted to reference data, either from experiments or higher levels of theory. Typically, they use a minimal atomic orbital basis set, parameterized multi-center integral approximations, and mean-field calculations based on Hartree-Fock (HF) theory or density-functional theory (DFT). The semiempirical H¨uckel method for π electrons was proposed only a year after HF theory in 1931, and it inspired more general models based on the zero-differential overlap (ZDO) approximation in the 1950’s. By the 1980’s, this had been further refined into the neglect of diatomic differential overlap (NDDO) approximation and developed into popular thermochemistry models such as AM1 and PM3, which are implemented in the MOPAC program