Assuming that the interaction between the magnetic moment and the external magnetic field obeys quantum mechanics, the microscopic model of paramagnetic medium can be established. The simple microscopic model is a nearly independent spin particle system in the external magnetic field. Statistical physical calculation results show that the relationship between magnetic susceptibility and magnetic field is generally nonlinear.

At zero temperature, the amount of decrease of the Gibbs function accompanying a chemical reaction is the heat released from the thermodynamic process, and the heat is defined as the zero-point heat. The zero-point heat consists in two parts, one is the difference between the thermodynamic zero-point internal energy of the reactant and that of the product in the chemical reaction, and another the mechanical energy of the volume changes of the reactant the product. For some systems, the Thomsen-Berthelot principle is applicable at room temperature and even higher, which means that zero-point heat plays significant roles at relatively high temperatures.