Accuracy and transferability of Gaussian approximation potential models for tungsten

We introduce interatomic potentials for tungsten in the bcc crystal phase and its defects within the Gaussian approximation potential framework, fitted to a database of first-principles density functional theory 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 observable only 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.

Figure 1

Fractional error in elastic constants and defect energies calculated with various interatomic potentials, as compared to the target DFT values.

Figure 2

Phonon spectrum of bcc tungsten calculated using GAP and FS potentials, and some reference DFT values.

Figure 3

Representation of the three different initial transition paths for the Peierls barrier calculation. Path A corresponds to the linear interpolation directly from the initial to the final state, whereas paths B and C are the two distinct linear interpolations that include a potential metastable state (corresponding to the hard structure of the dislocation core) at reaction coordinate $r=0.5$.

Figure 4

Top: The structure of the screw dislocation along the minimum energy path as it glides. Bottom: Peierls barrier evaluated using GAP and FS potentials, along with single-point checks with DFT in the 135-atom quadrupole arrangement.

Figure 5

Dislocation-vacancy binding energy evaluated using GAP and FS potentials. The top panels show the interpolated binding energy using a heat map; the graphs below are slices of the same along the dotted lines shown in the top panels.