arXiv subjects

Michael Wassermair

Publications and source records attributed to Michael Wassermair.

4 recordsLinked to original sources

arXiv2026

A non-reciprocal model for morphogenesis in symbiosis

The shape of a cell influences, and it is influenced by its interactions with its neighbours. Here, we introduce a coarse-grained computational model of non-reciprocal interactions between single-cell organisms to study emergent morphologies during symbiotic association. We show that the cell membrane can be remodelled into branched protrusions, invaginations, transient blebs and other dynamical morphologies that depend on the number of interacting partners, the asymmetry, and the magnitude of partnership activity. Our model finds a dynamical feedback between the local deformation of the membrane and its driving force, leading to membrane morphologies not reported in reciprocal systems with constant activity.

cond-mat.soft↗

arXiv2026

Radial Distribution Function in a Two Dimensional Core-Shoulder Particle System

An important quantity in liquid state theory is the radial distribution function $g(r)$. It can be calculated within the framework of classical density functional theory in two very distinct ways. In the test-particle route, one fixes a single fluid particle, turning it into an external potential in which the inhomogeneous structure of the fluid is calculated by minimising the functional. The second route to $g(r)$ in density functional theory employs the Ornstein-Zernike equation and the pair direct correlation function, that can be obtained from the second functional derivatives of the excess (over the ideal gas) free energy functional. Since typically an approximate excess free energy functional is employed, the test-particle route, which requires only one functional derivative, is more accurate than the Ornstein-Zernike route. Here we study a two dimensional core-shoulder particle system and find that in some circumstances the results from the Ornstein-Zernike route can be comparable in accuracy to the test-particle results for $r>σ$, the core diameter. We also examine in detail the asymptotic $r\to\infty$ decay of $g(r)$, finding a variety of possible decay wavelengths at different state points and state points where there is a crossover from one wavelength to a very different one. This behaviour is a signature pointing to the rich phase behaviour of the incipient solid phases.

cond-mat.soft↗

arXiv2026

Navigating complex phase diagrams in soft matter systems

Colloidal fluids can exhibit complex phase behavior and determining phase diagrams via experiments or computer simulations can be laborious. We demonstrate that the dispersion relation $ω(k)$, obtained from dynamical density functional theory for the uniform density system, is a highly versatile tool for {\it predicting} where in the phase diagram complex crystals form. The sign of $ω(k)$ determines whether density modes with wavenumber $k$ grow or decay over time. We demonstrate the predictive power by investigating the complex phase behavior of particles interacting via core-shoulder pair potentials. With complementary Monte Carlo simulations, we show that regions of the phase diagram where $ω(k)$ has one or several unstable (growing) wavenumbers are also where crystalline phases occur. Going further, by tuning these unstable wavenumbers via the interaction-potential and state-point parameters, we design systems with quasicrystals in the phase diagram. We identify a system with a certain shoulder-range exhibiting at least 10 different phases. Our general approach accelerates considerably the mapping of complex phase diagrams, crucial for the design of new materials.

cond-mat.soft↗

arXiv2024

Fingerprints of ordered self-assembled structures in the liquid phase of a hard-core, square-shoulder system

We investigate the phase ordering (pattern formation) of systems of two-dimensional core-shell particles using Monte-Carlo (MC) computer simulations and classical density functional theory (DFT). The particles interact via a pair potential having a hard core and a repulsive square shoulder. Our simulations show that on cooling, the liquid state structure becomes increasingly characterised by long wavelength density modulations, and on further cooling forms a variety of other phases, including clustered, striped and other patterned phases. In DFT, the hard core part of the potential is treated using either fundamental measure theory or a simple local density approximation, whereas the soft shoulder is treated using the random phase approximation. The different DFTs are bench-marked using large-scale grand-canonical-MC and Gibbs-ensemble-MC simulations, demonstrating their predictive capabilities and shortcomings. We find that having the liquid state static structure factor $S(k)$ for wavenumber $k$ is sufficient to identify the Fourier modes governing both the liquid and solid phases. This allows to identify from easier-to-obtain liquid state data the wavenumbers relevant to the periodic phases and to predict roughly where in the phase diagram these patterned phases arise.

cond-mat.soft↗