[CP2K-user] [CP2K:13504] Classical Forcefield

[Pierre Cazade]

Hi Thomas,

Thank you for your answer. I agree there's no way to reproduce the Thole 
potential with how the core-shell model is, to my understanding, 
implemented in CP2K. My question is how one can extract q_core, q_shell, 
and k_cs from, let's say, CHARMM or AMOEBA Thole parameters. For 
example, for sodium and SWM4 in CHARMM, one can find:

ATOM SOD  SODD     1.000  ALPHA -0.157

ATOM OH2  ODW      0.00000  TYPE DOH2    ALPHA -0.97825258 THOLE 1.3

I assume the first value means q=q_core+q_shell. Then, there's the 
polarizability which I assume is in A**3. In CHARMM, k_cs=1000 
kcal/mol/A**2 for all Drude oscillators. Finally, I think this 
relationship makes it possible to deduce k_cs and q_shell from one another:

k_cs = (q_shell)**2/alpha (obviously one takes the absolute value of the 
alpha provided by CHARMM)

The problem here is the homogeneity of the units. There's a missing 
conversion factor. So I wonder if anyone tried this before and what 
would it be? Finally there's the question of the sign of the q_shell. Is 
it given by the sign of the alpha parameter in CHARMM topology file? If 
so, it means all shells in CHARMM have a negative sign. Is it standard 
in the core-shell model for the charge of the shell to be negative?

Similar questions arise when checking AMOEBA. Again for water:

polarize    349          0.8370     0.3900    350
polarize    350          0.4960     0.3900    349

Here, the Thole factor (0.39) seems to be the same for all atom type 
save a couple of them. However, the polarizability is positive. Is it 
assumed that all shell charges are again negative or is the sign decided 
by other means? What is the meaning of the last column? Is it part of 
the exclusion list?

I do realize this is an obscure forcefield discussion and that CP2K 
forum might not be the best place for this.

My issue is that I need a polarizable model of water that can be used in 
CP2K and that is somewhat compatible with CHARMM36m for proteins. So, if 
anyone knows such a water model, I would be grateful if you could share it.

Thanks,
Pierre


On 10/06/2020 10:17, Thomas Kühne wrote:
> Dear Pierre,
>
> I don’t know for sure, but I doubt this is possible since Thole-based 
> polarization model
> typically entails a screened Coulomb potential to dampen the 
> intra-molecular interactions
> between the shells …
>
> Cheers,
> Thomas
>
>> Am 09.06.2020 um 18:49 schrieb Pierre-André Cazade 
>> <pierre.a... at gmail.com <mailto:pierre.a... at gmail.com>>:
>>
>> Dear Juerg,
>>
>> As follow up questions:
>>
>> To my knowledge, CP2K only uses a core-shell approach to model 
>> polarisability. It does not use Thole method at all. Am I correct?
>>
>> if so, is there a systematic way to adapt parameters from a Thole 
>> model (CHARMM polarisable, AMOEBA) to a core-shell model? Are there 
>> any plans to implement this feature (Thole polarisation method) in CP2K?
>>
>> Thanks again for your help.
>>
>> Best regards,
>> Pierre
>>
>> On Tuesday, June 9, 2020 at 3:31:54 PM UTC+1, Pierre-André Cazade wrote:
>>
>>     Dear Juerg,
>>
>>     Thank you for your answer. Another question, is it possible to
>>     have part
>>     of the ff provided by a file, let's say a charmm psf file, and
>>     the rest
>>     in CP2K input file?
>>
>>     Regards,
>>     Pierre
>>
>>     On 09/06/2020 14:25,hut... at chem.uzh.ch
>>     <mailto:hut... at chem.uzh.ch>wrote:
>>     > Hi
>>     >
>>     > besides simple pair potentials (with very general form of
>>     non-bonded terms),
>>     > there are FF of the form
>>     >
>>     > EAM  embedded atom model
>>     > COS  charge on spring (polarizable model)
>>     > Multipole models (up to quadrupoles)
>>     >
>>     > plus some other custom made FF.
>>     >
>>     > regards
>>     >
>>     > Juerg
>>     >
>>     > --------------------------------------------------------------
>>     > Juerg Hutter                         Phone : ++41 44 635 4491
>>     > Institut für Chemie C                FAX   : ++41 44 635 6838
>>     > Universität Zürich                   E-mail... at chem.uzh.ch
>>     <mailto:hut... at chem.uzh.ch>
>>     > Winterthurerstrasse 190
>>     > CH-8057 Zürich, Switzerland
>>     > ---------------------------------------------------------------
>>     >
>>     > -----cp... at googlegroups.com <mailto:cp... at googlegroups.com>wrote:
>>     -----
>>     > To: "cp2k" <cp... at googlegroups.com <mailto:cp... at googlegroups.com>>
>>     > From: "Pierre-André Cazade"
>>     > Sent by:... at googlegroups.com <mailto:cp... at googlegroups.com>
>>     > Date: 06/09/2020 02:41PM
>>     > Subject: [CP2K:13490] Classical Forcefield
>>     >
>>     > Dear CP2K users,
>>     >
>>     > I would like to know which types of classical forcefields CP2K
>>     is capable of handling. I am well aware of the types of input
>>     formats CP2K can read (Amber, Charmm, Gromos) but I am more
>>     interested in the nature of the forcefield. Aside from Amber,
>>     Charmm and Gromos forcefields, can CP2K use AMOEBA? Can it use a
>>     multipolar model? What are the limits in terms of potential
>>     forms? etc
>>     >
>>     > Regards,
>>     > Pierre
>>     >    --
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>>     >
>>     >
>>
>>     --
>>     Dr Pierre Cazade, PhD
>>     AD3-023, Bernal Institute,
>>     University of Limerick,
>>     Plassey Park Road,
>>     Castletroy, co. Limerick,
>>     Ireland
>>
>>
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-- 
Dr Pierre Cazade, PhD
AD3-023, Bernal Institute,
University of Limerick,
Plassey Park Road,
Castletroy, co. Limerick,
Ireland

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