Density functional theory (DFT)

Density functional theory is a computational quantum mechanics method used to calculate the electronic structure of atoms, molecules, and solids. Instead of solving the full many-electron wavefunction directly, an approach that becomes intractable as systems grow, it works from the electron density, a far simpler quantity, using an approximation called an exchange-correlation functional to represent electron-electron interactions.

The choice of functional trades accuracy against computational cost, and different functionals are better suited to different kinds of systems. DFT calculations scale better than higher-accuracy quantum chemistry methods but remain far more expensive than molecular dynamics, which uses empirical force fields instead of solving quantum-mechanical equations directly, so DFT is typically applied to smaller systems where that added accuracy matters.

DFT is a central tool in materials science, chemistry, and drug design for predicting energies, structures, and reactivity before physical synthesis, and its results increasingly train faster machine-learned interatomic potentials for larger-scale simulation. It relies on high-performance computing and is often one stage in a broader computational scientific workflow. Pitfalls include accuracy that depends heavily on the chosen functional, and known weaknesses, DFT notably struggles with weak van der Waals interactions and strongly correlated electron systems unless specifically corrected for them.