# ONETEP

ONETEP is a computer simulation program to perform linear-scaling first-principles calculations of materials. Using density functional theory (DFT), it can simulate a wide range of properties of materials proprieties including energetics, structure at the atomic level and, increasingly, spectroscopic properties. In contrast to conventional DFT implementations, the computational cost of a ONETEP calculation scales only linearly with system size.

ONETEP's linear scaling is achieved by computing the single-particle density matrix, rather than the single-particle wavefunctions. This density matrix is expressed in a Wannier function basis, comprised of functions localised in space, and these basis functions are coupled via a density-matrix kernel. The linear scaling is achieved when the density kernel is truncated at some fixed distance.

The linear scaling of ONETEP calculations makes it particularly suitable for DFT calculations of large systems, and ONETEP has been used successfully to study systems of tens of thousands of atoms.