Calculation Methods in Computational Chemistry

Computational chemistry uses several theoretical approaches to model molecular structure, energy, and properties, including Molecular Mechanics (MM), semi-empirical methods, ab initio quantum mechanics, and Density Functional Theory (DFT), each differing in accuracy and computational cost. Molecular Mechanics is a classical method based on empirical force fields that efficiently handles large systems such as proteins but cannot describe electronic effects or chemical reactions. Semi-empirical methods simplify the Schrödinger equation by introducing empirical parameters, allowing faster calculations while retaining partial electronic information, although their accuracy depends strongly on parameterization. Ab initio methods, such as Hartree–Fock, solve the Schrödinger equation from first principles without empirical parameters and provide a fundamental description of electronic structure, but they are computationally demanding and neglect electron correlation unless higher-level methods are applied. Density Functional Theory uses electron density as the main variable and offers a practical balance between accuracy and efficiency, making it widely used in computational chemistry, despite its dependence on the choice of exchange–correlation functional and limitations in describing dispersion and strongly correlated systems.