Molecular mechanics

Article By:

Baldridge, Kim Organic Chemistry Institute, University of Zurich, Zurich, Switzerland.

Amoreira, Celine Firmenich, Geneva, Switzerland.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.757328

An empirical computational method that provides structural, energetic, and property information about molecules. One simple way to consider molecules is as a collection of balls (atoms) held together by springs (bonds)—the basis of many molecular model kits (Fig. 1). Molecular mechanics offers a way to model the behavior of matter mathematically in this manner. Mechanical spring-based theory begins with a fundamental assumption that matter consists of atoms and that the potential energy of a collection of atoms can be defined for every set of positions. The collection of atoms is treated as a mechanical system moving within this potential energy, just as a clockwork's motions are determined by its spring potentials. Molecular mechanics methods are a natural outgrowth of concepts of bonding between atoms in molecules and van der Waals forces between nonbonded atoms. In 1930, T. L. Hill proposed the first such potential energy function made up of a simple representation of this type, including van der Waals interactions together with stretching and bending deformation functions. The idea was to minimize this energy function, leading to information about the structure and steric energy in congested molecules. Subsequent studies established more elaborate formulations of the potential-energy functional form, and were used to understand increasingly more detail about molecular systems, such as the equilibrium structure, energetics, thermodynamic properties, and vibrational spectra. Further work in the 1940s verified the theory for more complex reactions. See also: Chemical bonding; Energy; Van der Waals equation

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