It also enhances the direct transfer of the energy leading to the increase of thermal conductivity and shear viscosity. The calculated density and thermal expansion coefficient obtained from extension of Jacobsen equation of state for higher pressures and temperatures are presented in Figure 1. 2.2. Due to the repulsion of nitrogen atomic cores, free energy of nitrogen at higher pressure increases, especially in low temperatures. This increase is used in high pressure experiments to extend the stability range of GaN and plays crucial role in high pressure growth of gallium nitride. The nitrogen activity is presented in Figure 2 .
Heat capacity belongs to the properties which are least affected by high pressures.
The kinetic degrees of freedom contribution is determined by the equipartition principle. The potential degrees of freedom contribution is affected only by anharmonicity of the interaction potential close to the minimum. Therefore a small increase of the heat capacity for higher pressures is related to motion in the potential in the other molecules. On the other hand, the increase of the heat capacity at higher temperatures is due to the internal degrees of freedom of the nitrogen molecules that are induced for high temperatures. For higher temperatures nitrogen thermal conductivity was measured only for low pressures.