X-PLOR uses the conjugate gradient method by Powell (1977).
The minimization is started
from the atom properties X,Y,Z, and the minimized
coordinates are returned in X,Y,Z. Only the coordinates of
free atoms (i.e., not fixed atoms) will be modified during the
minimization (cf. Section 8.1). SHAKE
constraints are possible (cf. Section 8.2).
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.