Molecular Dynamics Simulations of Single-Layer Molybdenum Disulphide (MoS2): Stillinger-Weber Parametrization, Mechanical Properties, and Thermal Conductivity (1307.7072v2)

Abstract: We present a parameterization of the Stillinger-Weber potential to describe the interatomic interactions within single-layer MoS2 (SLMoS2). The potential parameters are fitted to an experimentally-obtained phonon spectrum, and the resulting empirical potential provides a good description for the energy gap and the crossover in the phonon spectrum. Using this potential, we perform classical molecular dynamics simulations to study chirality, size, and strain effects on the Young's modulus and the thermal conductivity of SLMoS2. We demonstrate the importance of the free edges on the mechanical and thermal properties of SLMoS2 nanoribbons. Specifically, while edge effects are found to reduce the Young's modulus of SLMoS2 nanoribbons, the free edges also reduce the thermal stability of SLMoS2 nanoribbons, which may induce melting well below the bulk melt temperature. Finally, uniaxial strain is found to efficiently manipulate the thermal conductivity of infinite, periodic SLMoS2.

• The paper introduces a novel SW potential for single-layer MoS2, validated against experimental phonon spectra to capture critical vibrational modes.
• MD simulations reveal free edge effects on mechanical properties, with Young’s modulus dropping in narrow nanoribbons and varying by edge orientation.
• Thermal conductivity is shown to be strain-sensitive, with an 8% uniaxial strain reducing conductivity by about 40%, enabling thermal property tuning.

Atomistic Simulations of Molybdenum Disulphide

This paper presents a Stillinger-Weber (SW) potential parameterization for single-layer molybdenum disulfide (SLMoS$_{2}$), enabling efficient molecular dynamics (MD) simulations to investigate its mechanical and thermal properties. The paper emphasizes the role of free edges on the mechanical and thermal behavior of SLMoS$_{2}$ nanoribbons, revealing significant edge effects on Young's modulus and thermal conductivity. Furthermore, the paper examines the manipulation of thermal conductivity through uniaxial strain in periodic SLMoS$_{2}$.

SW Potential Parameterization

The authors developed a SW potential parameterized by fitting to the experimentally-obtained phonon spectrum of SLMoS$$_{2}. The SW potential form includes two-body and three-body interaction terms, represented as:</p> <p>Two-body interaction:</p> <p>$$V_{2}=\epsilon A\left(B\sigma^{p}r_{ij}^{-p}-\sigma^{q}r_{ij}^{-q}\right)e^{[\sigma\left(r_{ij}-a\sigma\right)^{-1}]}$</p> <p>Three-body interaction:</p> <p>$V_{3}=\epsilon\lambda e^{\left[\gamma\sigma\left(r_{ij}-a\sigma\right)^{-1}+\gamma\sigma\left(r_{jk}-a\sigma\right)^{-1}\right]}\left(\cos\theta_{jik}-\cos\theta_{0}\right)^{2}$$</p> <p>Five distinct SW potential terms were introduced to capture essential interactions within SLMoS$$_{2}$:$V_{2}(Mo-S)$,$V_{2}(S-S)$,$V_{2}(Mo-Mo)$,$V_{3}(Mo-S-S)$, and$V_{3}(S-Mo-Mo)$$. The parametrization successfully reproduces the energy gap around 250 cm$$^{-1}$ and the crossover in the phonon spectrum, aligning with experimental data.</p> <h2 class='paper-heading' id='mechanical-properties'>Mechanical Properties</h2> <p>The SW potential accurately predicts the Young&#39;s modulus of SLMoS$_{2}$$with periodic boundary conditions (PBCs), yielding a value of 229.0 GPa, consistent with experimental measurements. MD simulations on SLMoS$$_{2}$ nanoribbons with free boundary conditions (FBCs) reveal significant edge effects on the Young&#39;s modulus, demonstrating a decrease in Young&#39;s modulus as the width of the nanoribbon decreases. The Young&#39;s modulus is smaller for armchair SLMoS$_{2}$than zigzag SLMoS$_{2}$$, and both converge to the same value as in the PBC calculation, i.e. 229.0 GPa, which corresponds to SLMoS$$_{2}$$without edge effects, as the width increases.</p> <h2 class='paper-heading' id='thermal-conductivity'>Thermal Conductivity</h2> <p>MD simulations using the parameterized SW potential investigate the thermal conductivity of SLMoS$$_{2}$$. The results indicate a notable reduction in thermal conductivity due to free edges, which induce a melting phenomenon at temperatures significantly below the bulk melting temperature. Uniaxial strain is shown to efficiently manipulate the thermal conductivity of infinite, periodic SLMoS$$_{2}$$, with an 8<h2 class='paper-heading' id='implications-and-future-directions'>Implications and Future Directions</h2> <p>This paper provides valuable insights into the atomistic behavior of SLMoS$$_{2}$$, offering a computationally efficient SW potential for MD simulations. The findings highlight the importance of considering edge effects when designing and utilizing SLMoS$$_{2}$$nanostructures for mechanical and thermal applications. The observed strain-dependent thermal conductivity opens avenues for tailoring thermal properties in SLMoS$$_{2}$$-based devices. Future research could focus on extending the SW potential to multi-layer MoS$$_{2}$ systems and exploring the influence of defects and chemical functionalization on mechanical and thermal properties.