[CP2K-user] [CP2K:19734] Correct TIP3P parameters

[Léon Luntadila Lufungula]

Hi Matthias,

Thanks for clarifying this for me. It was indeed a bit confusing, but I'm 
happy that I have a clear answer now!

Kind regards,
Léon

On Friday 12 January 2024 at 11:08:26 UTC+1 Krack Matthias wrote:

> Hi Léon
>
>  
>
> Yes, 110 kcalmol*rad^-2 and 900 kcal*Angstrom^-2 are correct. Note, that 
> the inputs in cp2k/tests are for code regression testing and the parameters 
> used therein are not reliable by contrast to the example inputs given in 
> the exercises. Unfortunately, many regression tests use this incorrect 
> flexible TIP3P force field. This is most likely a copy-paste error which is 
> indeed confusing for users. I will fix that.
>
>  
>
> Best 
>
>  
>
> Matthias
>
>  
>
> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Léon 
> Luntadila Lufungula <Leon.luntad... at uantwerpen.be>
> *Date: *Friday, 12 January 2024 at 10:09
> *To: *cp2k <cp... at googlegroups.com>
> *Subject: *Re: [CP2K:19729] Correct TIP3P parameters
>
> Hi Alin and Matthias,
>
>  
>
> Thanks for the quick reply, I didn't know that! If so, the 110/900 
> combination in the water.inp file should be correct then right? Still, in a 
> lot of input files in the tests folder like for example 
> cp2k/tests/Fist/regtest-4/H2O-1.inp (see attachment) the combination 55/450 
> is used. Can you explain why this is the case then?
>
>  
>
> Kind regards,
>
> Léon
>
>  
>
> On Friday 12 January 2024 at 10:02:01 UTC+1 Krack Matthias wrote:
>
> 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: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Léon 
> Luntadila Lufungula <Leon.luntad... at uantwerpen.be>
> *Date: *Friday, 12 January 2024 at 09:53
> *To: *cp2k <cp... 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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