SIESTA is both a method and the implementation of its software, to perform efficient electronic structure calculations and simulations ab initio of molecular dynamics of molecules and solids.
SIESTA's efficiency derives from the use of strictly localized base sets and the implementation of linear scaling algorithms that can be applied to suitable systems.
A very important feature of the code is that its accuracy and cost can be adjusted over a wide range, from quick exploratory calculations to highly accurate simulations that match the quality of other approaches, such as plane wave methods and all electronic methods.