**Please note: The FAQ pages at the HPCVL website are continuously being revised. Some pages might pertain to an older configuration of the system. Please let us know if you encounter problems or inaccuracies, and we will correct the entries.**

Crystal 98 is a programming package that is able to perform ab-initio calculations on periodic systems. It can be used to perform such calculations for systems that are periodic in zero (molecules), one (polymers), two (slabs, surfaces), and three (crystals) dimensions. Crystal performs self-consistent field calculations using either a Hartree-Fock, or a Kohn-Sham one-particle model Hamiltonian. The calculations are performed in a basis set of Bloch (ie, fully delocalized) orbitals, which are in term built from local atom-centered Gaussian-type basis functions (GTO's).

Crystal makes full use of the crystal symmetry, ie, the space group of the system under consideration. This means that for 3D systems 230 space groups can be specified, for 2D systems, it is 80 layer groups, for 1 D systems, 99 rod groups, and for 0D systems the familiar 45 point groups.

It is furthermore possible to derive slabs or clusters from crystalline structures, and to introduce defects and distortions into a structure.

Crystal also includes a properties package that allows the computation of a variety of bulk properties that are relevant for solid-state research. These include:

- Charge and spin densities
- X-ray structure factors
- multipole expansions
- Electrostatic potentials, electric fields, EFG's
- Band structure, density of states
- DFT correlation and exchange energies
- Hyperfine electron/nuclear spin interaction (isotropic and anisotropic), Fermi contact terms
- Electron momentum distributions, Compton profiles, reciprocal form factors

For a complete list of capabilities of Crystal, consult the Crystal manual (.pdf). Crystal 98 (1.0) was produced by *V.R. Saunders, R. Dovesi, C. Roetti, M. Causâ‚¬, N.M. Harrison, R. Orlando, and C. M. Zicovich-Wilson.*