Re: [AMBER] modified potentials

From: Irem Altan <>
Date: Fri, 29 Jul 2016 15:38:13 +0000


Thank you for your response. I’d like to zero out the potential beyond the first point the potential crosses the r-axis. Therefore there will only be a repulsive core remaining. This has to be specific for each atom type, as the point that crosses the axis is specific to the atom. Would LJEDIT be able to change the form of the potential function like this? If so, where can get more information as to how to use LJEDIT?


> On Jul 29, 2016, at 10:55 AM, David Cerutti <> wrote:
> In what way would you like to "truncate" the interaction? It is possible
> to specify NBFIX-like terms in Amber (LJEDIT), either as a new section of
> the parameter file (the thing that's called in order to build topologies)
> or, I think, using ParmEd. These LJEDIT terms are pair-specific
> Lennard-Jones interactions, so you could modify the interaction for
> particular types of atoms interacting with one another. The behavior is to
> leave the standard combining rules in effect unless otherwise stated, so
> all other interactions between said particles would stay the same.
> If the particles are few in number and always bonded to one another in
> fairly close proximity, you might be able to get away with some fancy NMR
> restraints that have no effect for r > L, where L is something like 4-8 A,
> and for r <= L the restraints attenuate or cancel out the effect of the
> Lennard-Jones terms you want to get rid of. I'd suggest trying LJEDIT
> first.
> Dave
> On Fri, Jul 29, 2016 at 9:52 AM, Irem Altan <> wrote:
>> Hi,
>> I was wondering, is it possible to use modified potentials in Amber for
>> nonbonded interactions? Specifically, I would like to truncate the LJ
>> potentials at the repulsive core for some protein atoms. Those atoms would
>> interact with the truncated potential amongst themselves, but use the full
>> form of the potential when interacting with other atoms. Is it possible to
>> do this with the tools available in Amber?
>> Best,
>> Irem
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