  We introduce interatomic potentials for tungsten in the bcc crystal phase and
its defects within the Gaussian Approximation Potential (GAP) framework, fitted
to a database of first principles density functional theory (DFT) calculations.
We investigate the performance of a sequence of models based on databases of
increasing coverage in configuration space and showcase our strategy of
choosing representative small unit cells to train models that predict
properties only observable using thousands of atoms. The most comprehensive
model is then used to calculate properties of the screw dislocation, including
its structure, the Peierls barrier and the energetics of the
vacancy-dislocation interaction. All software and raw data are available at
www.libatoms.org.
