Poisson solvers in QMMM

[Frank Uhlig]

Dear CP2k'lers,

related to a previous post (
https://groups.google.com/d/topic/cp2k/iMsqLpZnRyQ/discussion) I just
wanted to highlight the main problems again, because they might have been
hidden in the mess.

The QMMM electrostatic coupling is different for different Poisson solvers
if analogous inputs with Wavelet and Multipole solver are used. In the
example from the previous post (using Multipole solver) the QM images are
recoupled. If one just changes the Poisson solver to the Wavelet solver, no
recoupling of the QM images is performed. This behaviour then further
depends on the inclusion/exclusion of the non-optional section
%FORCE_EVAL%QMMM%PERIODIC.
The input can be changed in a way that one reproduces the total energies
with both Poisson solvers (up to ~0.01 eV).

This behaviour is counterintuitive, imo, and I would appreciate comments of
the developers, if it is intended, if I am doing something wrong etc pp

Cheers,

Frank
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