[gmx-developers] Wall interaction with tabulated potential

[Berk Hess]

Hi,

But epsilon should be 1/4 to match 1/r^12, 1/r^6.

Berk

On Feb 5, 2016 11:17 AM, Sudharsan Pandiyan <sudharsan.pandiyan at chem.kuleuven.be> wrote:
>
> Hi,
>
> I generated the tables using the csg_call routine from the VOTCA-CSG program and I input 1.0 for sigma and epsilon values in topol.top file (1 also for the combination rule). I also generated the LJ particle interaction table for interaction between the particles in the simulation box, which gives exactly same potential energy for both table potential and 12-6 potential. But the wall-particle interaction produces different values.
>
> Sincerely,
>
> Sudharsan
>
> ________________________________
> From: gromacs.org_gmx-developers-bounces at maillist.sys.kth.se [gromacs.org_gmx-developers-bounces at maillist.sys.kth.se] on behalf of Sudharsan Pandiyan [sudharsan.pandiyan at chem.kuleuven.be]
> Sent: 05 February 2016 11:08
> To: gmx-developers at gromacs.org
> Subject: Re: [gmx-developers] Wall interaction with tabulated potential
>
> Hi Berk,
>
> Thank you very much for quick reply. But, I input 1.0 for sigma and epsilon values. Still the problem persists.
>
> Sincerely,
>
> Sudharsan
> ________________________________
> From: gromacs.org_gmx-developers-bounces at maillist.sys.kth.se [gromacs.org_gmx-developers-bounces at maillist.sys.kth.se] on behalf of Berk Hess [hess at kth.se]
> Sent: 05 February 2016 10:42
> To: gmx-developers at gromacs.org
> Subject: Re: [gmx-developers] Wall interaction with tabulated potential
>
> Hi,
>
> You should not put sigma and epsilon in the table. The dispersion and repulsion table get multiplied by C6 and C12, respectively.
>
> Cheers,
>
> Berk
>
> On 2016-02-05 09:57, Sudharsan Pandiyan wrote:
>>
>> Dear Gmx developers,
>>
>> I am trying to simulate a wall option using tabulated potentials option. But it gives different LJ potential values when I compare 12-6 potential with the tabulated potential (where the table was generated using same sigma and epsilon values that were used for 12-6 potential). 
>>
>> I intend to modify my table potential later so I wanted to make sure that it produces correct result. But my test shows that there is a difference between 12-6 and tabulated potentials for wall interaction. Could you please explain what is the difference and how can I get the correct potential energy for tabulated potentials?
>>
>> PS: In the manual, its written that both 9-3 and 10-4 are integrated over the surface area and 12-6 potential was applied directly with the z-distance. But how the tabulated potential is represented? (section 7.3.20)
>>
>>
>> Thank you very much for your time and support.
>>
>> Sincerely,
>>
>> Sudharsan
>>
>>
>>
>