[CP2K-user] [CP2K:19727] Correct TIP3P parameters

[Krack Matthias]

Dear Léon

Note that LAMMPS uses a different potential definition<https://docs.lammps.org/angle_harmonic.html>. By contrast to CP2K, LAMMPS includes the prefactor ½ into the constant K.

HTH

Matthias

From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Léon Luntadila Lufungula <Leon.luntadilalufungula at uantwerpen.be>
Date: Friday, 12 January 2024 at 09:53
To: cp2k <cp2k at googlegroups.com>
Subject: [CP2K:19726] Correct TIP3P parameters
Dear all,

Just a quick question about the parameters for the TIP3P forcefield. In the example files (see attached water.inp) of the exercise<https://www.cp2k.org/exercises:2019_uzh_acpc2:ex02> on molecular simulation of water the TIP3P model is used to simulate water. In the input file, I noticed that the force constant of the H-O-H bend and the H-O bond are 110 rad^-2kcalmol and 900 angstrom^-2kcalmol, respectively. However, when looking online for the parameters like on the lammps documentation<https://docs.lammps.org/Howto_tip3p.html>, I find that these values are actually half of what is defined in the input, i.e., 55 rad^-2kcalmol and 450 angstrom^-2kcalmol, respectively... Is this indeed an error in the input file or am I missing something here? Most water input files I see in the tests/Fist folder also contain the smaller values for the force constants.

Kind regards,
Léon
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