Re: [AMBER] the difference between proper torsion and improper torsion

From: James Maier <>
Date: Wed, 25 Sep 2013 11:58:36 -0400

Proper torsion involves four consecutively bonded atoms i-j-k-l.

Improper torsion is basically any other torsion calculated based on four
atoms not successively bonded. Say j is not just bound to i, but also to
m. You could defined improper torsion i-j-k-m to control the torsional
difference between i-j-k-l and m-j-k-l (or substitute any other atom
bounded to k for l). This is useful for planar things, including the
peptide bond in the amino acid backbone.

Generally people devote more attention to proper torsions when refining
force fields because most "interesting" motions are around single bonds.
 That being said, there could be occasion to target improper torsions, and
this obviously needs to be done when developing an altogether new force

To summarize: proper torsion controls affinity between things on opposite
ends of a bond (e.g., i and l). Improper torsion usually controls affinity
between things on the same end of a bond (e.g., i and m).

Hope this helps,


On Wed, Sep 25, 2013 at 11:43 AM, Ming Huang

> Hi,
> I have a simple question, what is the difference between proper torsion and
> improper torsion.
> I know, in mathematics, they may share the same formula and in chemistry,
> torsion is used to describe the rotation along one bond.
> Does torsion has some advantage in optimization, force field, compared to
> improper torsion?
> Many thanks,
> Ming
> --
> Ming Huang
> BioMAPS, Rutgers University
> 610 Taylor Road
> Piscataway, New Jersey, 08854
> Cell Phone: 612-208-7832
> E-mail: <>
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Received on Wed Sep 25 2013 - 09:00:05 PDT
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