If OCTTargetOperator = oct_tg_velocity, and
OCTScheme = oct_cg or OCTScheme = oct_bfgs
then you must supply the target in terms of the ionic velocities AND
the derivatives of the target with respect to the ionic velocity components.
The derivatives are supplied via strings through the block
OCTVelocityDerivatives.
Each velocity component is supplied by "v[n_atom,vec_comp]",
while n_atom is the atom number, corresponding to the
Coordinates block, and vec_comp is the corresponding
vector component of the velocity. The first line of the
OCTVelocityDerivatives block contains the derivatives
with respect to v[1,], the second with respect to v[2,] and so
on. The first column contains all derivatives with respect v[,1],
the second with respect to v[,2] and the third w.r.t. v[*,3].
As an example, we show the OCTVelocityDerivatives block
corresponding to the target shown in the OCTVelocityTarget
help section: