[CP2K-user] [CP2K:13543] Single Molecule Molecular Dynamics

[Thomas Kühne]

Dear Lucas, 

have you conducted the geometry optimization with exactly the same settings, 
i.e. basis set, PW cutoff, EPS_SCF, etc.? Since your system has so few DOFs, 
fluctuations will be large and conservation by cancellation inherently poor. 
Hence, with such a tiny system I would rather stick with NVT instead of NVE + 
viral theorem and not use ANGVEL_ZERO … 

Greetings, 
Thomas

> Am 21.06.2020 um 07:14 schrieb Lucas Lodeiro <eluni... at gmail.com>:
> 
> 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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