[CP2K-user] [CP2K:19756] Correct TIP3P parameters

[Léon Luntadila Lufungula]

Dear Matthias,

Thanks for clarifying this for me, I'll keep it in mind in the future when 
setting up my forcefield parameters.

Kind regards,
Léon

On Saturday 13 January 2024 at 10:18:21 UTC+1 Krack Matthias wrote:

> Dear Léon
>
>  
>
> I have to correct my statement concerning the regression test inputs. The 
> &BEND and &BOND section parameters in these inputs (e.g. in 
> Fist/regtest-4/H2O-1.inp) are correct for the flexible TIP3P model, because 
> the default value for the KIND keyword 
> <https://manual.cp2k.org/cp2k-2024_1-branch/CP2K_INPUT/FORCE_EVAL/MM/FORCEFIELD/BEND.html#CP2K_INPUT.FORCE_EVAL.MM.FORCEFIELD.BEND.KIND> 
> in these sections is CHARM and not HARMONIC as I wrongly assumed. So you 
> have to take care which KIND of forcefield you are using when you set these 
> parameters.
>
>  
>
> Best regards
>
>  
>
> 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 12:24
> *To: *cp2k <cp... at googlegroups.com>
> *Subject: *Re: [CP2K:19734] Correct TIP3P parameters
>
> 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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