Omar-Farouk Adesida | Searcharxiv

arXiv2025

Revisiting the Phase Diagram of Hard Sphere Dumbbells with Nested Sampling: Known Phases and New Packing Variants

We explore the use of the nested sampling technique to sample the configuration space of non-spherical hard particles. We employ the technique on the hard dumbbell system consisting of two hard spheres connected by a rigid bond, and investigate the phase stability across a wide pressure range and for bond lengths from completely overlapping to tangential hard spheres. Nested sampling recovers all previously identified features of the phase diagram and identifies a family of new packing variants. The fluid phase, plastic crystal, close packed solid phases and aperiodic crystal are all sampled, and the transition points between these are mapped. Our results show good agreement with predictions made by existing equations of state, and former Monte Carlo simulations. Nested sampling also identified a close packed structure with Pnma symmetry which has not previously been considered.

cond-mat.soft↗

arXiv2024

Phase transitions and cluster structures of the new finite range Lennard-Jones like model

In the current work we revisit the pair-potential recently proposed by Wang et al. (Phys. Chem. Chem. Phys. 10624, 22, 2020) as a well defined finite-range alternative to the widely used Lennard-Jones interaction model. The advantage of their proposed potential is that it not only goes smoothly to zero at the cutoff distance, hence eliminating inconsistencies caused by different treatments of the truncation, but with changing the range of the potential, it is capable of describing soft matter-like behaviour as well as traditional "Lennard-Jones-like" properties. We used the nested sampling method to perform an unbiased sampling of the potential energy surface, and mapped the pressure-temperature phase diagram of a range of truncation distances. We found that the interplay between the location of the energy minimum and interaction range has a complex and strong effect on both the structural and thermodynamic properties of the condensed phases. We discuss the appearance of the liquid-vapour co-existence line and critical point at longer interaction ranges, as well as the relatively small changes in the melting line. We present the ground state diagram, demonstrating that different close-packed polytypic phases appear to be global minima for the model at different pressure and cutoff values, similar to what had been shown in case of the Lennard-Jones model. Finally, we compare the lowest energy structure of some of the N < 60 clusters to that of the known minima of Lennard-Jones and Morse potential, using different cutoff values, revealing a behaviour closely resembling that of the Morse clusters.

cond-mat.mtrl-sci↗