[CP2K-user] Single Molecule Molecular Dynamics

[Lucas Lodeiro]

Hi all,
I want to perform single molecule molecular dynamics.
First I do a convergence test for cutoff, cell size and poisson solver. I
read in old mails, that MT is better than WAVELET for MD, due to the first
is translational invariant.
After that I start a MD from the optimized molecular geometry at the same
level of theory. I want to obtain statistical information for a given
temperature (300K for example), I think an NVT is not well behaved for a
single molecule, then I ran NVE MD. As the geometry is at the minimum, I
start with 2*T (where T is the target temperature) thinking in virial
theorem (at equilibrium equal potential and kinetic energy).
But the system is not converging (the average temperature) at the desired
temperature. It shows a weird temperature oscillation (different as
expected due to bond oscillation), it present in some moment higher
temperature than the initial and a potential energy lower than the
initial... Also, the molecular rotation exhibits variations along the MD
and translation in the box. For that I start a new MD with the same INPUT
and geometry, adding ANGVEL_ZERO. The MD starts without rotation but in 300
fs it starts to rotate.
I attach the files for both MD.

I read about the geometrical constraints, it would be useful for diatomic
molecules, but for H2O or complexer molecules is not a solution.

Has somebody faced these problems? some advice?

regards
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