Rigid-Body Minimization

The rigid-body method minimizes the six rotational and translational degrees of freedom for each specified group of atoms; i.e., the groups of atoms are treated as rigid bodies. The complete energy function $E_{TOTAL}$ is used. The rotational parameters are the three Eulerian angles $\theta_1,\theta_2,\theta_3$ for a rotation around the geometric centers of the rigid group. The three translational parameters are x,y,z in the Å frame. Parts of the molecule that are not specified in any GROUp statement will remain fixed. The constraints fix statement (Section 8.1) has no influence on rigid-body minimization (except for the default group selection). Upon completion of the last energy calculation, symbols are declared that contain the computed energy terms. The name of the symbols is given by $$<$energy-term$>$ (see Section 4.5). The overall energy (Eq. 4.1) is stored in the symbol $ENER; the rms gradient is stored in $GRAD. The value of the second energy function (Eq. 4.26) is returned in the symbol $PERT.