Re: [AMBER] How does tleap detect improper torsions?

From: David A Case <>
Date: Thu, 24 Sep 2020 15:20:56 -0400

On Thu, Sep 24, 2020, Brian Radak wrote:
>Do I understand correctly that tleap will in fact (silently) change the
>explicit improper definitions based on the alphabetical rule? For purely
>planar terms I don't know off hand if this actually matters (probably not
>for energies, maybe for forces?)

Here's my understanding: tleap figures out what impropers there should
be in this way: for each central atom that has exactly three bonded
neighbors, look in the force field for an improper in which the three
non-central atoms obey the alphabetical rule.

     If it finds a match, it uses it;
     If it fails to find a match, that's OK: it assumes that there is not
        supposed to be such an improper, because it is not found in the
        force field. For things with sp2 hybridization, it will print a

I'm not sure exactly what you mean by "change the explicit improper
definitions", because I'm not sure what is meant by "explicit improper
definitions". Leap expects the force field developer to enter torsion
terms in the proper order, and (to my knowledge) it doesn't try to "fix" any
non-alphabetical entries.

If there ever is any uncertainty, use parmed to inspect your prmtop file
to see what terms are really there.


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Received on Thu Sep 24 2020 - 12:30:02 PDT
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