On the existence of thermodynamically stable rigid solids.Customarily, crystalline solids are defined to be rigid since they resist changes of shape determined by their boundaries.  However, rigid solids cannot exist in the thermodynamic limit where boundaries become irrelevant.  Here, we show that a thermodynamic collective variable may be used to quantify particle rearrangements that occur as a solid is deformed at zero strain rate.  The rigid phase becomes thermodynamically stable when an external field, which penalizes particle rearrangements, is switched on. 
THERM