CASTEP
CASTEP is a leading code for calculating the properties of materials from first principles. Using density functional theory (DFT), it can simulate a wide range of properties of materials proprieties including energetics, structure at the atomic level, vibrational properties, electronic response properties etc. In particular it has a wide range of spectroscopic features that link directly to experiment, such as infra-red and Raman spectroscopies, NMR, and core level spectra.
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 for large simulations 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 - 20,000 atoms depending on which chemical elements are present and the computational resources available.
For more information on CASTEP, see the dedicated CASTEP website.