Possibility for ML of QM Force Sample Clauses

Possibility for ML of QM Force. ‌ In most covalent materials, quantum mechanical force exerted on atom depend on the local atomic environment formed by the neighbouring atoms. Such QM force can gener- ally be approximated within a certain precision by the calculation upon a finite cluster with a cutoff number of neighbouring atoms. As displayed in panel (a) of Fig.5.2 for Silicon, for local cluster calculation around a centre atom with neighbouring atoms cut- off at above 8 ˚A in spherical radius (around 4 bond hops), the DFTB forces converge within a precision of 0.05 eV/˚A in magnitude, or less than 4% in relative error. At 10 ˚A or 5 bond hops, the relative error decreases to 1% or ∼ 0.01 eV/˚A in magnitude. In Panel (b) the force convergence is tested on more general structural forms. Similarly, for cluster above cutoff radius of 8 ˚A, forces convergence with error less than 0.05 eV/A˚. For the MLOTF in this thesis work, we will typically adopt a cluster cutoff at 8 ˚A for Si calculations, while a Gaussian noise σerror = 0.05 eV/A˚ is assumed for the QM force data. Force convergence at a cutoff cluster size suggests it is computationally robust to derive a scheme only taking into account the atomic environments pertinent to the QM force. Especially in the non-periodic large system calculations, such kind of cluster calculation within a reasonably cutoff radius is usually used instead of doing the self-consistent calculation treating the system as a whole [12, 13].