arXiv subjects

Jonathan Busse

Publications and source records attributed to Jonathan Busse.

2 recordsLinked to original sources

arXiv2025

Exact lattice summations for Lennard-Jones potentials coupled to a three-body Axilrod-Teller-Muto term applied to cuboidal phase transitions

This work provides a rigorous analysis of Bain-type cuboidal lattice transformations, which connect the face-centered cubic (fcc), mean-centered cubic (mcc), body-centered cubic (bcc) and axially centered cubic (acc) lattices. Our study incorporates a general $(n,m)$ Lennard-Jones two-body potential and a long-range repulsive Axilrod-Teller-Muto (ATM) three-body potential. The two-body lattice sums and their meromorphic continuations are evaluated to full precision using super-exponentially convergent series expansions. Furthermore, we introduce a novel approach to computing three-body lattice sums by converting the multi-dimensional sum into an integral involving products of Epstein zeta functions. This enables us to evaluate three-body lattice sums and their meromorphic continuations to machine precision within minutes on a standard laptop. Using our computational framework, we analyze the stability of cuboidal lattice phases relative to the close-packed fcc structure along a Bain transformation path for varying ATM coupling strengths. We analytically demonstrate that the ATM cohesive energy exhibits an extremum at the bcc phase and show numerically that it corresponds to a minimum for repulsive three-body forces along the Bain path. Our results indicate that strong repulsive three-body interactions can destabilize the fcc phase and render bcc energetically favorable for soft LJ potentials. However, even in this scenario, the bcc phase remains susceptible to further cuboidal distortions. These results suggest that the stability of the bcc phase is, besides vibrational, temperature, and pressure effects, strongly influenced by higher than two-body forces. Because of the wrong short-range behavior of the triple-dipole ATM model the LJ potential is limited to exponents $n>9$ for the repulsive wall, otherwise one observes distortion into a set of linear chains collapsing to the origin.

cond-mat.mtrl-sci↗

arXiv2024

Computation and properties of the Epstein zeta function with applications to quantum systems

The Epstein zeta function generalises the classical Riemann zeta function to oscillatory lattice sums in higher dimensions and has recently emerged as a key tool in the simulation of long-range interacting classical and quantum many-body systems. Its computation and analytic properties are therefore of significant interest, yet a rigorous and comprehensive treatment has been lacking. We address this gap by introducing a superexponentially convergent algorithm, complete with error bounds, for computing the Epstein zeta function in any dimension with arbitrary real parameters. Our approach is accompanied by a detailed analysis of the analytic properties of the Epstein zeta function. We first present a concise reformulation of its meromorphic continuation, functional equation, and symmetries. We then establish, for the first time, its joint holomorphic continuation in all parameters and offer a complete characterization of the resulting complex singularity structure, which governs convergence rates in numerical algorithms based on the function. Recognizing that the function can be decomposed into power-law singularities and a regularised analytic part, we provide an algorithm for removing singularities without cancellation error. This facilitates the evaluation of integrals and enables fast precomputations through interpolation methods. We present the first high-performance implementation for arbitrary real arguments in EpsteinLib, a C library with Python and Julia bindings, and rigorously benchmark its performance and accuracy, achieving full-precision evaluation against known analytic results in dimensions 1,2,3,4,6, and 8 and against an arbitrary precision implementation across the entire parameter range. Finally, we apply our methods to the computation of quantum dispersion relations in spin systems and Casimir energies in three-dimensional geometries.

math.NA↗