The subscripts on the various theta's refer to different combinations of 3 atoms (I,J,K,L) used to form a particular angle. E.g. Theta_IJL is the angle formed by atoms I,J,L with J in the middle. Theta1, -theta2, theta3 are the equilibrium positions of those angles. +theta2, theta3 are the equilibrium positions of those angles. Again, +atom J (the 2nd atom in the quadruplet) is the atom of symmetry in the +theta angles, since it is always the center atom. +
+Note that defining 4 atoms to interact in this way, does not mean that +bonds necessarily exist between I-J, J-K, or K-L, as they would in a +linear dihedral.
See (Sun) for a description of the COMPASS class2 force field.
diff --git a/doc/improper_class2.txt b/doc/improper_class2.txt index 2edb552a81..038656e160 100644 --- a/doc/improper_class2.txt +++ b/doc/improper_class2.txt @@ -32,12 +32,18 @@ refers to the angle between the plane of I,J,K and the plane of J,K,L, and the bond JK lies in both planes. Similarly for X_KJLI and X_LJIK. Note that atom J appears in the common bonds (JI, JK, JL) of all 3 X terms. Thus J (the 2nd atom in the quadruplet) is the atom of -symmetry in this formulation. +symmetry in the 3 X angles. The subscripts on the various theta's refer to different combinations of 3 atoms (I,J,K,L) used to form a particular angle. E.g. Theta_IJL is the angle formed by atoms I,J,L with J in the middle. Theta1, -theta2, theta3 are the equilibrium positions of those angles. +theta2, theta3 are the equilibrium positions of those angles. Again, +atom J (the 2nd atom in the quadruplet) is the atom of symmetry in the +theta angles, since it is always the center atom. + +Note that defining 4 atoms to interact in this way, does not mean that +bonds necessarily exist between I-J, J-K, or K-L, as they would in a +linear dihedral. See "(Sun)"_#Sun for a description of the COMPASS class2 force field.