Study Of Isothermal Equation Of State Of Aluminium

The equation of state is used to describe the relation among the pressure, temperature and volume of the matter in a thermodynamic equilibrium system, and it is also a fundamental research in physics. With the high-speed development of the natural science and engineering technology, the properties and states of the material system under the high pressure environment are required in some certain circumstance. However, the simulation of the experiment under this kind of environment is very difficult, so many works which have been carried out are various kinds of theoretical calculation by putting forward correct models of matter's microstructure and then obtaining the macroscopical data of these processes using statistic physics and quantum mechanics.In present paper, two different methods are used to calculate the isothermal equation of state respectively. First, we calculate isothermal relation of the density and pressure including the contribution of the electron, phonon and photon using average-atom(AA) model, which gives the wavefunctions and orbital energies for the bound electrons by solving the Dirac equation and the average occupation numbers at each orbital of each kind of atom determined by the Fermi-Dirac distribution. Second, we calculate the lattice constant, bulk modules and static phase transition of Aluminum in the framework of density functional theory (DFT) using the augmented plane wave plus local orbitals (APW+lo) method with generalized gradient approximation (GGA) for the exchange-correlation potential, and then give the relation of pressure-volume at 0 K. We also evaluate the vibrational contribution of the lattice ion to the total free-energy according to the free-volume theory, and give the relation of pressure-volume at T = 1 eV. Comparison is given between these two results, experimental results and that from Sesame database.