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TORSION

Calculate a torsional angle.

This command can be used to compute the torsion between four atoms or alternatively to calculate the angle between two vectors projected on the plane orthogonal to an axis.

The atoms involved can be specified using
ATOMS the four atoms involved in the torsional angle
Or alternatively by using
AXIS two atoms that define an axis. You can use this to find the angle in the plane perpendicular to the axis between the vectors specified using the VECTOR1 and VECTOR2 keywords.
VECTOR1 two atoms that define a vector. You can use this in combination with VECTOR2 and AXIS
VECTOR2 two atoms that define a vector. You can use this in combination with VECTOR1 and AXIS
Options
NUMERICAL_DERIVATIVES ( default=off ) calculate the derivatives for these quantities numerically
NOPBC ( default=off ) ignore the periodic boundary conditions when calculating distances
COSINE

( default=off ) calculate cosine instead of dihedral

Examples

This input tells plumed to print the torsional angle between atoms 1, 2, 3 and 4 on file COLVAR.

t: TORSION ATOMS=1,2,3,4
# this is an alternative, equivalent, definition:
# t: TORSION VECTOR1=2,1 AXIS=2,3 VECTOR2=3,4
PRINT ARG=t FILE=COLVAR