Cuboidal bcc to fcc Transformation of Lennard-Jones Phases under High Pressure Derived from Exact Lattice Summations

The stability of the body-centered cubic (bcc) compared with the face-centered cubic (fcc) phase at finite pressures is investigated through exact lattice summations using a general (a, b) Lennard-Jones potential (a > b > 3). At zero pressure, the bcc phase is unstable or, at best, metastable for unphysical low values of the exponents (a, b) of the Lennard-Jones potential. From Helmholtz free energy calculations, we demonstrate that the stability of the bcc phase decreases with increasing pressure, with the metastable phase persisting into the high-pressure range up to a high pressure limit at exponent a = 7.6603891 for the repulsive wall. The transition path is chosen to be of Bain type, connecting smoothly the two phases through a series of body-centered tetragonal (cuboidal) lattices.

Automated summary

This study investigates the stability of the body-centered cubic (bcc) phase compared with the face-centered cubic (fcc) phase at finite pressures. The results show that the stability of the bcc phase decreases with increasing pressure. This research provides important insights into the understanding of crystal phase stability.