ddCOSMO Surface Area Incorrect

[lukaswittmann]

The surface area written into the xtb.cosmo file is wrong for any overlapping spheres.

Example: Surface area (Ang^2) of O2 from distance 0 to 4 Angs in 0.01 Ang steps (default):

It is discontinuous and qualitatively wrong. One would expect a nearly linear growth from a to 2a. This is correct, e.g., with ALPB.
The respective routine misses the inclusion of the switching function ui (via self%ddCosmo%ui(ig, iat)); with inclusion (swi), however, the surface area is still incorrect.

The respective implementation in our tblite ddx development branch delivers the correct result.