arXiv subjects

Ville Jantunen

Publications and source records attributed to Ville Jantunen.

4 recordsLinked to original sources

arXiv2026

Multiscale modelling of diffusion and retention of hydrogen in multi-occupancy traps in irradiated bcc metals

We use molecular dynamics simulations to directly compute the effective diffusivity of hydrogen gas atoms in homogeneous distributions of monovacancies in tungsten and vanadium, and voids in tungsten. Rather than fitting the results to an Arrhenius law, we compare to an analytic approximation for the effective diffusivity recently derived for multi-occupancy traps [Kaur et al (2025), Phys. Rev. Mater. 9:125404]. We find good agreement between full atomistic simulation and our theory, validating the analytic model for diffusivity for materials containing nanoscale defects characteristic of radiation damage. There are no parameters fitted, only physically motivated quantities that can be computed with static density functional or atomistic potential calculations. In this study we prove rapid convergence of hydrogen trap occupation to the steady state using lattice kinetic Monte Carlo, the spontaneous emergence of voids in tungsten using atomistic simulation with empirical potentials, and molecular hydrogen formation in voids using molecular dynamics. We conclude with a prediction for diffusion and retention of hydrogen in voids in tungsten starting from first principles. This work shows that not only is the analytic form for diffusivity and retention in multi-occupancy traps a practical scheme for making predictive simulations of hydrogen isotope diffusion and retention in irradiated microstructures, derived and parameterized from first principles, it is superior to existing single-occupancy trap formalisms.

cond-mat.mtrl-sci↗

arXiv2025

Beyond dpa: an atomistic framework for a quantitative description of radiation damage in YBa2Cu3O7

Radiation damage in high-temperature cuprate superconductors represents one of the main technological challenges for their deployment in harsh environments, such as fusion reactors and accelerator facilities. Their complex crystal structure makes modeling irradiation effects in this class of materials a particularly demanding task, for which existing damage models remain inadequate. In this work, we develop an atomistic-based approach for describing primary radiation damage in YBa2Cu3O7, by coupling Molecular Dynamics and Binary Collision Approximation simulations in a way that makes them complementary. When integrated with Primary Knock-on Atom spectra obtained from Monte Carlo codes, our results establish a framework for multiscale modeling of radiation damage, enabling quantitative estimates of several damage descriptors, such as defect production, defect clustering, and the effective damaged volume for any specific irradiation conditions where collision cascades dominate. This computational approach is suitable for the prediction of irradiation effects in any complex functional oxide, with applications ranging from aerospace to nuclear fusion and high-energy physics.

cond-mat.supr-con↗

arXiv2024

High-dose long-time defect evolution in tungsten studied by atomistically informed Object Kinetic Monte Carlo simulations

Irradiation of materials in nuclear test reactors and power plants is known to alter the properties of the material. The irradiation event happening at pico- or nanosecond time scales are affecting the evolution and properties of the material on macroscopic timescales. Classical Molecular Dynamics simulations, which can capture the cascade event, are typically limited to nanosecond time scales, resulting in high dose rates. To achieve experimental dose rates, larger-scale models like Object Kinetic Monte Carlo are used, while they lack atomistic detail. The exact evolution of cascades in the vicinity of pre-existing defects is known to affect the defects formed, and the structure and morphology of the defects produced are crucial to know for determining macroscopic material behavior. Here we introduce a novel approach to integrate full Molecular Dynamics-based cascades into Object Kinetic Monte Carlo to achieve accurate dose rates, with the atomistic level accuracy of cascade overlap in tungsten. Our study reveals that incorporating full cascades significantly influences defect concentration levels. Not only is the concentration affected, but also the cluster statistics. We observe both that the full cascade can promote vacancy clustering at low temperatures and it can split existing voids at higher temperatures. These effects are missing in conventional Object Kinetic Monte Carlo simulations. This can be especially important in more complex materials, where many cascade-overlap effects are present.

cond-mat.mtrl-sci↗

arXiv2024

Insights on molecular P implantation for scalable spin-qubit arrays

Quantum information technologies hold immense promise, with quantum computers poised to revolutionize problem-solving capabilities. Among the leading contenders are solid-state spin-qubits, particularly those utilizing the spin of phosphorous donors (31 P ). While significant progress has been made in enhancing quantum coherence and qubit control, challenges persist, notably in achieving precise and scalable P placement in Si substrate. This paper investigates by means of molecular dynamics the use of molecular PF2 ions for implantation, aiming to reduce placement uncertainty while maintaining detection efficiency. We examine energy transfer, molecule integrity, implantation profiles, electronic signal components, and stable damage. Among other things we find that the assumption that the molecule only breaks apart immediately due to the presence of an a-SiO2 layer on the surface of the crystal and that the intensity of the electronic signal from ion-solid interactions does not correlate necessarily with the penetration depth of P.

physics.comp-ph↗