arXiv subjects

Livia B. Partay

Publications and source records attributed to Livia B. Partay.

5 recordsLinked to original sources

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↗

arXiv2022

Carbon phase diagram with empirical and machine learned interatomic potentials

In the present work we detail how the many-body potential energy landscape of interatomic potentials for carbon can be explored by utilising the nested sampling algorithm, allowing the calculation of their pressure-temperature phase diagram up to high pressures. We present a comparison of three interatomic potential models, Tersoff, EDIP and GAP-20, focusing on their macroscopic properties, particularly on their melting transition and on identifying thermodynamically stable solid structures up to at least 100 GPa. The studied models all form graphite structures upon freezing at lower pressure, then the diamond structure as the pressure increases. We were able to locate the transition between these phases in case of the Tersoff and EDIP models. We placed particular focus on the state-of-the-art machine learning (ML) model, GAP-20, and calculated its phase diagram up to 1 TPa to evaluate its predictive capabilities well outside of the model's fitting conditions. The phase diagram showed a remarkably good agreement with the experimental phase diagram up to 200 GPa, despite a variety of unexpected graphite layer spacing. Above that nested sampling identified two novel stable solid structures, a strained diamond structure and above 800 GPa a strained hexagonal-close-packed structure. However, the stability of these two phases were not confirmed by DFT calculations, highlighting potential routes to further improve the ML model.

cond-mat.mtrl-sci↗

arXiv2018

Direct computation of the quantum partition function by path-integral nested sampling

In the present work we introduce a computational approach to the absolute rovibrational quantum partition function using the path-integral formalism of quantum mechanics in combination with the nested sampling technique. The numerical applicability of path-integral nested sampling is demonstrated for small molecules of spectroscopic interest. The computational cost of the method is determined by the evaluation time of a point on the potential-energy surface (PES). For efficient PES implementations, the path-integral nested-sampling method can be a viable alternative to the direct Boltzmann summation technique of variationally computed rovibrational energies, especially for medium-sized molecules and at elevated temperatures.

quant-ph↗

arXiv2018

On the performance of interatomic potential models of iron: comparison of the phase diagrams

In order to study the performance of interatomic potentials and their reliability at higher pressures, the phase diagram of four different embedded-atom type potential models of iron is compared. The calculations were done by the nested sampling technique in the pressure range 0.1 GPa-100 GPa. The low pressure stable structure is found to be the body- centred cubic in all cases, but the higher pressure phases show a great variation, being face-centred cubic, hexagonal close-packed and - at very low temperatures - different body-centred tetragonal phases are observed as well. The melting line is overestimated considerably for three of the models, but for the one where liquid properties had been taken into account during the potential fitting process, the agreement with experimental results is good, even at very high pressures.

cond-mat.mtrl-sci↗