Melting point#Predicting the melting point of substances .28Lindemann.27s criterion.29

The Lindemann criterion (after Frederick Lindemann ) is a criterion for the melting of solids: If the maximum displacement of the lattice atoms is greater than, where a is the lattice constant, breaking the fixed order of the crystal together.

For example, even at absolute zero, the vibration amplitude of helium atoms at atmospheric pressure is about ( ZPE ). It can not form a solid phase, therefore, this occurs bar on only at pressures above 25.