The phase transition temperature in zirconium metal from the classical molecular dynamics method

Abstract

The Helmholtz free energy is determined in order to describe the bcc-hcp phase transition. We used the classical molecular dynamics method to evaluate the components of the Helmholtz free energy such as the internal energy and the entropy composed of the vibrational entropy and the electronic entropy. The vibrational entropy includes harmonic and anharmonic effects. The harmonic vibrational entropy is calculated from the phonon density of states, which comes from the velocity autocorrelation function. The anharmonic vibrational entropy can be calculated from the anharmonic free energy. The electronic entropy is evaluated from the electronic density of states. We found that the vibrational entropy difference between the bcc and the hcp phases at transition temperature is 0.20 kB, compared with 0.26 kB from experiments, and the transition temperature is 1047?210 K, compared with 1135 K from experiments. The results from classical Molecular Dynamics are in good agreement with the experimental results.