Atomistic

Atomistic is an adjective describing approaches, models, or explanations that consider matter at the level of individual atoms and their interactions. The term has historical roots in atomism, a philosophy that posits that all substances are composed of small, indivisible units and void. In modern science, atomistic descriptions underpin atomic theory and contrast with continuum or macroscopic models that treat materials as uniform media.

In practice, atomistic modeling is central to chemistry, physics, and materials science. It describes systems by specifying the positions and interactions of atoms, using either classical or quantum mechanical methods. Classical approaches rely on force fields to model interatomic forces in molecular dynamics or Monte Carlo simulations. Quantum-mechanical methods include ab initio molecular dynamics and density functional theory, which treat electrons explicitly to varying degrees of approximation. Atomistic simulations are used to predict structures, dynamics, reaction mechanisms, and thermodynamic properties of molecules, crystals, polymers, and biomolecules.

Advantages of atomistic methods include detailed mechanistic insight and the ability to link microscopic behavior to macroscopic observables. Limitations include high computational cost, dependence on the accuracy of interaction potentials or exchange-correlation functionals, and practical timescale or system-size constraints. Atomistic modeling is often complemented by coarse-grained or continuum approaches to balance detail and efficiency.