L-BFGS with an initial diagonal inverse hessian equal to 0.01 distance squared
per energy. At each step after the initial, the initial inverse hessian, which
determines the scale of the problem, is updated according to:

$$ H_0 = \frac{\Delta x \cdot \Delta x}{\Delta x \cdot \Delta g} $$

with $\Delta x = x_k - x_{k-1}$ and $\Delta g = g_k - g_{k-1}$.

The memory length was set to 100 steps and the maximum move
distance was 0.2 distance units. The LBFGS history was reset when the angle
between the descent direction and the force became greater than 90º or a
step greater than the max move was taken.