  Theoretical studies on the experimental feasibility of hypothetical Zeolitic
Imidazolate Frameworks (ZIF) have focused so far on relative energy of various
polymorphs, by energy minimization at the quantum chemical level. We present
here a systematic study of stability of 18 ZIFs as a function of temperature
and pressure, by molecular dynamics simulations. This approach allows us to
better understand the limited stability of some experimental structures upon
solvent or guest removal. We also find that many of the hypothetical ZIFs
proposed in the literature are not stable at room temperature. Mechanical and
thermal stability criteria thus need to be considered for the prediction of new
MOF structures. Finally, we predict a variety of thermal expansion behavior for
ZIFs as a function of framework topology, with some materials showing large
negative volume thermal expansion.
