Thermal and Mechanical Properties

Abstract

The thermal and mechanical properties of molecular assemblies are very important. Since these assemblies have some degrees of freedom in their electronic and lattice systems, their thermal and mechanical properties give clues to the characteristics of their electronic structure and lattice dynamical behavior. In molecular assemblies, molecules form solid crystals in which intramolecular interactions between atoms are more than one order of magnitude stronger than the intermolecular interactions, whose strength ranges from about 0.1 to 1 eV. An assembly of atoms forms molecular orbitals with energies of eV, and then interactions between the molecular orbitals of adjacent molecules form the electronic structure of a molecular crystal. In terms of lattice dynamical behavior, the energies of intramolecular vibrations are approximately 0.1 eV, which are well separated from the energy range of the intermolecular vibrations with strengths around of 0.01 eV. These unusual features of the electronic structure and lattice dynamics give specific characteristics to molecular assemblies which are different from those of ordinary ionic crystals or metal crystals which do not have molecular units.