Asap is a tool for doing atomic-scale computer simulations (mainly molecular dynamics) using classical potentials (mainly Effective Medium Theory).
Asap is intended to work as an energy calculator in connection with the Atomic Simulation Environment (ASE). However, some parts of the ASE are either extended or reimplemented for reasons of efficiency and ease-of-use on parallel computers.
Do I need Asap?
If you are installing the Campos software to do Density Functional Theory calculations with Dacapo, you do not need to install Asap.
How does Asap relate to the ASE and to Dacapo?
Asap and Dacapo are both tools for calculating the forces and energies on atoms. They both require the ASE to be useful, since the ASE contains objects and algorithms necessary to do atomic-scale simulations.
Dacapo used Density Functional Theory, i.e. quantum mechanics, to calculate the energies. It is therefore slow but accurate, and can in principle handle all elements of the periodic table. Calculations with Dacapo are limited to a few tens of atoms, or perhaps a hundred atoms on a parallel computer.
Asap uses a classical potential, the Effective Medium Theory, to calculate the energies. This is an approximation that only works for some elements (Ni, Cu, Pd, Ag, Pt, Au, Mg), but then it gives reasonably accurate results very quickly. With Asap you can do molecular dynamics of a million atoms on a single PC (if you are patient), or tens of millions on a parallel computer.