[CP2K-user] SCF convergence issues

[Ryan Rogers]

 <cp... at googlegroups.com>
Dear CP2K community,

I am having issues in DFT QM/MM force calculations on molecular crystals of
paracetamol (acetaminophen). I am describing here the two problems I most
often experience. I am currently unable to identify the cause or any
pattern in the problems I encounter. The root of the problems could be
something other than what I identify below; I am pointing out the
problematic features in the output that are most obviously to me. All input
and output files are included.

*1. Total energy falls into "hole" and never converges.
(CP2K_problemTotalE_conf_0636.tar.gz)*
Personal experience tells me to expect a "Total energy" for these systems
on the order of -2,000 (Hartree) and a "Hartree energy" on the order of
+2,000 (Hartree).
In these jobs, I find an initial "Hartree energy" on the order of >-10,000
(Hartree), which appears to send the SCF wavefunction optimization down a
path of non-convergence, in which the "Total energy" can easily become on
the order of -100,000 (Hartree) before I kill the job.

*2. Total charge density on grids grows too large.
(CP2K_problemEGrids_conf_0623.tar.gz)*
In these jobs, the Total energy looks reasonable, and the Convergence looks
promising in the few SCF cycles of steps.
However, the total Change never drops below my threshold, and eventually
the "Total charge density on r-space/g-space grids" becomes much too large.

My configurations are extracted from MD trajectories, so the atoms have
perturbations from their perfect crystal positions. One confusing
observation is that very similar QM/MM configurations selected from other
frames of the same trajectory often have no problems.
My configurations are constructed from a cluster of several molecules in
the QM region with usually another layer usually 1-2 molecules thick making
up the MM region. (In the attached sample images, the size of the stick
molecules alludes to a larger/smaller basis set used, while the MM atoms
are denoted as points.) Because I am not including integer numbers of unit
cells, I am not using PBC.

Any advice about both/either problem will be greatly appreciated!

Sincerely,
Ryan Rogers
rr... at nyu.edu <trr... at email.uark.edu>
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