Classical Forcefield

[Pierre-André Cazade]

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 

[Thomas Kühne]

Dear Pierre, 

to the best of my knowledge AMOEBA and multipolar FF’s aren’t implemented. 

However, in the subsections NONBONDED, BOND, BEND etc. within 

MM/FORCEFIELD there are quite a lot of potential forms that can be defined 

beyond the FFs you have mentioned. 

Greetings, 

Thomas

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==============================

Thomas D. Kühne

Dynamics of Condensed Matter

Chair of Theoretical Chemistry

University of Paderborn

Warburger Str. 100

D-33098 Paderborn

Germany

tdku...@mail.upb.de

+49/(0)5251/60-5726

[hut...@chem.uzh.ch]

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: hut...@chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp...@googlegroups.com wrote: -----
To: "cp2k" <cp...@googlegroups.com>
From: "Pierre-André Cazade"
Sent by: cp...@googlegroups.com
Date: 06/09/2020 02:41PM
Subject: [CP2K:13490] Classical Forcefield

[Pierre Cazade]

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

--
Dr Pierre Cazade, PhD
AD3-023, Bernal Institute,
University of Limerick,
Plassey Park Road,
Castletroy, co. Limerick,
Ireland

[Pierre-André Cazade]

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 

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[hut...@chem.uzh.ch]

Hi

we don't do any development of classical FF in my group.

regards

Juerg Hutter

--------------------------------------------------------------
Juerg Hutter Phone : ++41 44 635 4491
Institut für Chemie C FAX : ++41 44 635 6838
Universität Zürich E-mail: hut...@chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

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From: "Pierre-André Cazade"
Sent by: cp...@googlegroups.com

Date: 06/09/2020 06:49PM
Subject: Re: [CP2K:13498] Classical Forcefield

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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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[Thomas Kühne]

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

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[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

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