The quantum states of macroscopic systems

The whole of this chapter is concerned with the quantum states of macroscopic systems. Tl is not a very familiar idea because the chemist or engineer becomes accustomed to thinking of the quantum states of single molecules, for which approximate solutions of Sohro-dinger s equation may be obtained. However, these solutions have significance only if the molecules are independent and this is not the case in liquids or solids. The form of statistical mechanics to be aimed at is one which will apply to liquids and solids, as well as to gases. 

In a diatomic molecule, as is well known, it is not possible to ascribe sets of quantized energy levels to each of the two atoms the potential energy of interaction is mutual and, therefore, a separate 

For a mass of solid or liquid, containing a total of, say, 10 electrons and nuclei, the possible quantum states could be obtained, in principle, by solving a Schrddinger differential equation containing 3 X10 terms, one for each of the necessary co-ordinates. However, for the present purposes it is not necessary to suppose that this equation has been solved all that we need for the statistical theory is the idea that these quantum states exist. 

---