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Re: [lammps-users] pair style table for Coulombic and dispersion pair interactions
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Re: [lammps-users] pair style table for Coulombic and dispersion pair interactions


From: Jo <jojo412202@...24...>
Date: Tue, 5 Sep 2017 19:09:52 -0400

Hello,

I have a bit of confusion about the documentation regarding using tables, found in pair_table:

If your tabulated potential(s) are designed to be used as the short-range part of one of the long-range solvers specified by the kspace_style command, then you must use one or more of the optional keywords listed above for the pair_style command. These are ewald or pppm or msm or dispersion or tip4p. This is so LAMMPS can insure the short-range potential and long-range solver are compatible with each other, as it does for other short-range pair styles, such as pair_style lj/cut/coul/long. Note that it is up to you to insure the tabulated values for each pair of atom types has the correct functional form to be compatible with the matching long-range solver.

What does "compatible with the matching long-range solver" entail?  How can I ensure that it matches with the long range solver?  The table I made of the short range potential is simply the original coulombic interaction dampened at short distances.

Below is what I think might be how it works:

In creating the table, I assume I can use the functional form of the real space ewald solver: 0.5*qq/r*erfc(alpha*r), where alpha is the real/reciprocal space partition parameter (1/cutoff).  From what I understand, I must match this partition parameter/cutoff by making the kspace_modify gewald value the same, thus matching the cutoffs.  Is this correct and is there more matching I need to check to make sure it is compatible?

Additionally, if I would like to use tables for both coulombic and dispersion potentials, can I combine the energies in 1 table to be used in the realspace short range?  I was unable to find information about making 2 sets of tables compatible in the documentation.

Thank you in advance!

J

On Tue, Sep 5, 2017 at 5:23 AM, Michał Kański <michal.kanski@...4225...0...> wrote:

The manual answers those questions:

http://lammps.sandia.gov/doc/pair_hybrid.html

http://lammps.sandia.gov/doc/kspace_style.html

 

Michal

 

 

From: Jo
Sent: wtorek, 5 września 2017 05:10
To: lammps-users@...396...sourceforge.net
Subject: [lammps-users] pair style table for Coulombic and dispersion pair interactions

 

Hello,

 

I would like to implement a simulation that utilizes tables for the pair potentials for both the short range coulombic interactions and the dispersion interactions.  The tables I made for the coulumbic interactions are short range and I would like for it to be combined with the ewald long range calculations using kspace.  I have not been able to get both sets of tables to work in the input file.

 

What I have tried:

 

hybrid overlay table linear 1500 ${cutoff} coul/long${cutoff}

pair modify pair coul/long table linear 1500

 

However, I get errors saying illegal pair_style.  How should I implement both tables at the same time?  How can I let lammps know that one set of the tables is for coulombic together with kspace ewald, and the other set is for dispersion?  

 

Also, for the coulombic tables, I made the potentials simply from (q*q/r)*damping_factor, is this adequate for it to fit together with kspace ewald?

 

Thank you!

 

Jo