Speaker:
Dr Andrew Duff, Department of Materials, Imperial College London, UK
Abstract:
A new method for calculating ab initio thermodynamic properties of materials is presented. The new approach, termed TU-TILD (two-stage upsampled thermodynamic integration using Langevin dynamics) captures the full anharmonicity of the lattice vibrations and provides at least an order of magnitude improvement in efficiency compared to the UP-TILD approach on which it is based. Using TU-TILD, free energies can be calculated up to the melting point at the full accuracy of the underlying ab initio theory– in the present case, density functional theory –overcoming limitations of the widely used quasiharmonic approximation, whilst significantly closing the gap in computational efficiency between fully anharmonic and quasiharmonic methodologies. The new approach is used to calculate the thermodynamic properties of zirconium carbide, with the calculated thermal expansion found to be in better agreement with experiment, and the heat capacity reproducing rather closely a CALPHAD estimate. Furthermore, a factor of improvement in efficiency of ~50 is achieved compared to the UP-TILD approach, demonstrating the potential of the new approach in bringing such calculations into the mainstream of materials modelling applications.