PREDICTING THE OCCURRENCE OF REFLECTION TWINS

This paper describes a method for predicting which surfaces of a cryst al can form reflection twins. The algorithm has been successfully appl ied to six inorganic crystal systems ranging from simple salts (corund um and rutile) to more complicated systems containing molecular ions ( aragonite, gibbsite, sodium oxalate and zircon). Our approach calculat es the difference between the attachment energies of twinned and untwi nned growth slices. The occurrence of planes that result in a small di fference of energy (<1% of the intermolecular lattice energy) correlat es with all the commonly observed twinning in these systems.