xnn.common.models.electrostatics.coulomb_dsf#

xnn.common.models.electrostatics.coulomb_dsf(charges, edge_index, r, alpha, cutoff, k_e=14.39964547846902)[source]#

Per-atom share of the damped shifted-force Coulomb energy over a neighbor list.

Each pair within cutoff contributes q_i q_j phi(r) with the force-shifted screened kernel

phi(r) = erfc(alpha r) / r - erfc(alpha r_c) / r_c + (r - r_c) [erfc(alpha r_c) / r_c^2 + 2 alpha / sqrt(pi) exp(-alpha^2 r_c^2) / r_c]

(zero value and slope at r_c), and every atom carries the self term -[erfc(alpha r_c) / (2 r_c) + alpha / sqrt(pi)] q_i^2. The pair terms are accumulated in float64.

Parameters:

charges (Tensor) – Partial charges (N,).
edge_index (Tensor) – Ordered pairs (2, E) as [src, dst]; both directions of a pair are expected, as a neighbor list provides them.
r (Tensor) – The pair distances (E,).
alpha (float) – Damping parameter in 1/Angstrom.
cutoff (float) – The real-space cutoff r_c in Angstrom; pairs beyond it are ignored, so the neighbor list may be longer.
k_e (float, optional) – The Coulomb constant, by default COULOMB_CONSTANT.

Returns:

Per-atom energies (N,) in eV, float64.

Return type:

Tensor