iSwiG cavity

iSwiG is the switching Gaussian surface-discretization approach [LH10] for van der Waals type cavitites. Each atomic sphere is discretized using Lebedev quadrature grids. Every grid point is assigned a smooth weight given by a product of error-function switches from the neighbouring spheres, so buried points fade out continuously. Points whose switching value (or area) falls below a cutoff are removed.

The implemented variant supports also analytic nuclear derivatives using adaptive radii [WGRR25].

The implementation lives in src/moist/cavity/iswig.f90; the cavity type is cavity_type_iswig and the constructor is new_cavity_iswig.

Settings

All three settings are optional constructor arguments.

nleb (integer, default 110)

Number of Lebedev quadrature points per atomic sphere; the primary accuracy/cost setting. Must be one of the supported sizes: 14, 26, 50, 110, 194, 302, 434, 590, 770, 974, 1202. Any other value raises an error, because each grid has a fitted Born zeta (the Gaussian width scale).

cut_f (real, default 1.0e-10)

Switching-value cutoff. A point is kept only if its switching function exceeds this value. Used when cut_a is not set.

cut_a (real, default 0.0)

Area cutoff. When greater than zero it replaces cut_f: a point is kept only if its switched area (Lebedev area times switching value) exceeds this value.