Ab initio random structure searching (AIRSS) is a very simple, yet powerful and highly parallel, approach to structure prediction. The concept was introduced in 2006 [1] and its philosophy more extensively discussed in 2011 [2].

Random structures—or more precisely, random “sensible” structures—are generated and then relaxed to nearby local energy minima. Particular success has been found using density functional theory (DFT) for the energies, hence the focus on “ab initio” random structure searching. The sensible random structures are constructed so that they have reasonable densities, and atomic separations. Additionally they may embody crystallographic, chemical or prior experimental/computational knowledge. Beyond these explicit constraints the emphasis is on a broad, uniform, sampling of structure space.

AIRSS has been used in a number of landmark studies in structure prediction, from the structure of SiH₄ under pressure [1], to providing the theoretical structures which are used to understand dense hydrogen (and anticipating the mixed Phase IV) [3], incommensurate phases in aluminium under terapascal pressures [4], and ionic phases of ammonia [5]. The approach naturally extends to the prediction of clusters/molecules, defects in solids [6], interfaces and surfaces (which can be thought of as interfaces with vacuum) [7].

The AIRSS package is tightly integrated with the Castep first principles total energy code. However, it is relatively straightforward to modify the scripts to use alternative codes to obtain the core functionality. xxx_relax scripts for vasp, pp3, gulp, psi4, and lammps are provided and integrated with the airss.pl script.

Licence and Citation

The AIRSS package is released under the GPL 2.0 licence. See the LICENCE file for more details. You are not required to, but you might consider citing references [1] and [2] in any work that makes use of the AIRSS package.


(1) C.J. Pickard and R.J. Needs, Phys. Rev. Lett., 97, 045504 (2006) [Link]
(2) C.J. Pickard and R.J. Needs, J. Phys.: Condens. Matter, 23, 053201 (2011) [Link]
(3) C.J. Pickard and R.J. Needs, Nat. Phys., 3, 473 (2007) [Link]
(4) C.J. Pickard and R.J. Needs, Nat. Mater., 9, 624 (2010) [Link]
(5) C.J. Pickard and R.J. Needs, Nat. Mater., 7, 775 (2008) [Link]
(6) A.J. Morris, C.J. Pickard and R.J. Needs, Phys. Rev. B, 78, 184102 (2008) [Link]
(7) G. Schusteritsch and C.J. Pickard, Phys. Rev. B, 90, 035424 (2014) [Link]