[Paper Review] Direction dependent thermal conductivity of monolayer phosphorene: parameterization of Stillinger-Weber potential and molecular dynamics study

Wen Xu, Liyan Zhu+3 more|arXiv (Cornell University)|May 26, 2015

Thermal properties of materials1 references4 citations

TL;DR

This study develops a parameterized Stillinger-Weber potential for monolayer phosphorene to enable equilibrium molecular dynamics simulations, revealing a strong direction-dependent thermal conductivity with values of 152.7 W/mK along the zigzag direction and 33.0 W/mK along the armchair direction, resulting in an anisotropy ratio of five. The anisotropy arises primarily from differences in phonon group velocities, with effective phonon mean free paths of 141.4 nm (zigzag) and 43.4 nm (armchair).

ABSTRACT

A Stillinger-Weber interatomic potential is parameterized for phosphorene. It well reproduces the crystal structure, cohesive energy and phonon dispersion predicted by first-principles calculations. The thermal conductivity of phosphorene is further explored by equilibrium molecular dynamics simulations adopting the optimal set of potential parameters. At room temperature, the intrinsic thermal conductivities along zigzag and armchair directions are about 152.7 and 33.0 W/mK, respectively, with a large anisotropy ratio of five. The remarkably directional dependence of thermal conductivity in phosphorene, consistent with previous reports, is mainly due to the strong anisotropy of phonon group velocities, and weak anisotropy of phonon lifetimes as revealed by lattice dynamics calculations. Moreover, the effective phonon mean free paths at zigzag and armchair directions are about 141.4 and 43.4nm, respectively.

Motivation & Objective

• To develop a transferable Stillinger-Weber interatomic potential for monolayer phosphorene that accurately captures its structural and energetic properties.
• To investigate the intrinsic thermal conductivity of phosphorene using equilibrium molecular dynamics simulations.
• To understand the origin of the strong anisotropy in thermal transport by analyzing phonon group velocities and lifetimes.
• To quantify the effective phonon mean free paths along different crystallographic directions in phosphorene.

Proposed method

• A Stillinger-Weber potential was parameterized using first-principles data for phosphorene, including lattice constants, cohesive energy, and phonon dispersion relations.
• Equilibrium molecular dynamics simulations were performed at room temperature using the optimized potential parameters to compute thermal conductivity.
• Lattice dynamics calculations were employed to analyze phonon group velocities and lifetimes along the zigzag and armchair directions.
• The thermal conductivity was calculated using the Green-Kubo formalism applied to the heat current autocorrelation function.
• The effective phonon mean free path was estimated from the ratio of thermal conductivity to the product of specific heat, group velocity, and phonon density of states.
• The results were validated by comparing the potential's predictions with first-principles data for structural and vibrational properties.

Experimental results

Research questions

• RQ1 What is the thermal conductivity of monolayer phosphorene along the zigzag and armchair crystallographic directions?
• RQ2 Why does phosphorene exhibit such strong anisotropy in thermal transport properties?
• RQ3 How do phonon group velocities and lifetimes contribute to the direction-dependent thermal conductivity in phosphorene?
• RQ4 What are the effective phonon mean free paths along the zigzag and armchair directions in phosphorene?
• RQ5 Can a Stillinger-Weber potential be accurately parameterized to reproduce first-principles results for phosphorene's thermal and vibrational properties?

Key findings

• The thermal conductivity of monolayer phosphorene is 152.7 W/mK along the zigzag direction and 33.0 W/mK along the armchair direction at room temperature.
• The anisotropy ratio of thermal conductivity between zigzag and armchair directions is approximately five.
• The strong anisotropy is primarily due to the large difference in phonon group velocities, while phonon lifetimes show only weak anisotropy.
• The effective phonon mean free path is 141.4 nm along the zigzag direction and 43.4 nm along the armchair direction.
• The parameterized Stillinger-Weber potential accurately reproduces the crystal structure, cohesive energy, and phonon dispersion from first-principles calculations.
• The study confirms that phonon group velocity anisotropy dominates over lifetime anisotropy in determining the overall thermal conductivity anisotropy in phosphorene.