public void setXRange(double newXMin,
Defines the region atoms must be selected from. The atom is chosen
randomly. If the atom is not in the region, repeated attempts are
made until one is found or maxAttempts is reached.
If newXMax > newXMin, then newXMax > x > newXMin.
If newXMax < newXMin, then newXMax < x < newXMin (the region spans the
boundary, excluding the middle of the box)