Condensed Matter Physics Semina - Roman Martoňák (11.11.2022)
Friday 11.11.2022 at 14:00, Lecture room F2/272
By: Roman Martoňák
Simulations of structural phase transitions in crystals
Structural phase transitions in crystals, induced by temperature or pressure, represent highly interesting phenomena important for fundamental as well as practical reasons. At the same time, however, they present notable challenges for both analytical and numerical modeling. I will start by reviewing difficulties related to simulations of these transitions by standard sampling techniques such as plain molecular dynamics. I will then focus on the application of enhanced sampling approaches such as metadynamics and on the choice of appropriate collective variables. I will present results of our recent work  where we proposed a NPT metadynamics simulation scheme for pressure-induced structural phase transitions, using coordination number and volume as collective variables, and applied it to the reconstructive structural transformation B1-B2 in NaCl. By studying systems with size up to 64000 atoms we reached a regime beyond collective mechanism and observed transformations proceeding via nucleation and growth. We also revealed the crossover of the transition mechanism from Buerger-like for smaller systems to Watanabe-Tolédano for larger ones. The scheme is likely to be applicable to a broader class of pressure-induced structural transitions, allowing study of complex nucleation effects and bringing simulations closer to realistic conditions.
 Matej Badin and Roman Martoňák, Phys. Rev. Lett. 127, 105701 (2021)