migration.md

Migration Guide

This document lists changes you need to make when upgrading to a new version of TinyFF. Minor versions upgrades should maintain backward compatibility. Only when the major version changes, you may need to make changes to code using TinyFF

Upgrading from TinyFF 1 to 2

The required changes are relatively minor:

• You can import all the relevant functions and classes from the top-level tinyff package. For example, change from:

  from tinyff.atomsmithy import build_fcc_lattice
  from tinyff.forcefield import CutOffWrapper, LennardJones, ForceField
  from tinyff.neighborlist import NBuildSimple

  to

  from tinyff import build_fcc_lattice, CutOffWrapper, LennardJones, ForceField, NBuildSimple

  Note that the old tinyff.forcefield has been split into two modules: forcefield and pairwise. By using the top-level imports, your code becomes independent of such internal details.

• When creating a ForceField instance, the nbuild argument must be specified with a keyword. For example, change from:

  ff = ForceField([LennardJones(1.0, 1.0)], NBuildSimple(rmax))

  to

  ff = ForceField([LennardJones(1.0, 1.0)], nbuild=NBuildSimple(rmax))

• When computing energies (and forces), you need to call the ff.compute method, instead of using the force field object as a function. If you want to compute forces and pressure, this must be requested explicitly. By default, version 2 will only compute the energy. For example, change from:

  energy, forces, pressure = ff(atpos, cell_lengths)

  to

  energy, forces, pressure = ff.compute(atpos, cell_lengths, nderiv=1)

• The pair potentials have undergone a similar change. If you want to calculate the derivative, you need to ask for it explicitly. By default, only the energy is computed. For example, change from:

  lj = LennardJones(1.0, 1.0)
  e, g = lj.compute(dist)

  to

  lj = LennardJones(1.0, 1.0)
  e, g = lj.compute(dist, nderiv=1)