# Software

The UKCP consortium has a particular emphasis on developing software for high-performance computational simulations of material and chemical properties. There are three major simulation packages developed by UKCP and its members:

Each of these programs is based on Density Functional Theory (DFT). DFT is a reformulation of quantum mechanics which allows calculations of the behaviour of electrons in real chemicals and materials. The difference between the three programs lies in their representation of the electronic states, and the methods they use to solve the resulting equations.

CASTEP uses a plane-wave basis to describe the wavefunction. It is capable of simulating any kind of chemical or material (within the limits of present DFT approximations), but the computational time it takes scales approximately cubically with the size of the system's unit cell. In practice this places an upper limit on the application of CASTEP of 1,000 - 10,000 atoms depending on which chemical elements are present and the computational resources available.

In contrast to CASTEP's cubic scaling, CONQUEST and ONETEP use different algorithms which scale linearly with system size. Whilst these algorithms are slower for small systems, their improved scaling means that as larger and larger systems are studied they eventually overtake the more conventional methods of CASTEP. Both CONQUEST and ONETEP have been used to study systems of many tens of thousands of atoms.