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Conjugate Gradient Minimization

      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.

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