TORSION IMPROPER

 NAME
TORSION IMPROPER – Read proper torsion potential

 SYNOPSIS

• AMBER form [cosine]
  TORSION IMPROPER
  ...
  typ1  typ2  typ3  typ4   $K_{\phi}$  $n$  $\gamma$   [cosine]
  ...
  END
• CHARMM form [harmonic]
  TORSION IMPROPER
  ...
  typ1  typ2  typ3  typ4   $K_{\phi}$  $angle$  [harmonic]
  ...
  END

 DESCRIPTION
typ1, typ2, typ3 and typ4 are four character strings, not to exceed 7 characters, indicating the atom types of the four atoms involved in the torsion interaction (a x string is taken to be as a wild card indicating $any$ atom) For improper torsions, ORAC allows both the CHARMM–like form (a simple harmonic potential) or the AMBER–like form (a torsional potential):

For the CHARMM form $K_{\phi}$ must be given in Kcal mol$^{-1}$ rad$^{-2}$, while $angle$ is the equilibrium angle of the improper torsion in degree.

For the AMBER form the meaning of the symbol are identical to those described in the TORSION PROPER directive.

 EXAMPLE

TORSION IMPROPER
x    x    ca   h4       1.1000   2.0  180.0 cosine
x    x    ca   h5       1.1000   2.0  180.0 
ck   cb   n*   ct       1.0000   2.0  180.0 cosine
cm   c    n*   ct       1.0000   2.0  180.0 cosine
ha   cpa  cpa  cpm      29.40    0.0  harmonic
ha   cpb  c    c        20.00    0.0  harmonic
ha   ha   c    c        20.00  180.0  harmonic
END