**Anomalous strain effect on the thermal conductivity of borophene: a
reactive molecular dynamics study**

B Mortazavi and MQ Le and T Rabczuk and LFC Pereira, PHYSICA E-LOW- DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 93, 202-207 (2017).

DOI: 10.1016/j.physe.2017.06.012

Borophene, an atomically thin, corrugated, crystalline two-dimensional boron sheet, has been recently synthesized. Here we investigate mechanical properties and lattice thermal conductivity of borophene using reactive molecular dynamics simulations. We performed uniaxial tensile strain simulations at room temperature along in-plane directions, and found 2D elastic moduli of 188 N m(-1) and 403 N m(-1) along zigzag and armchair directions, respectively. This anisotropy is attributed to the buckling of the borophene structure along the zigzag direction. We also performed non-equilibrium molecular dynamics to calculate the lattice thermal conductivity. Considering its size- dependence, we predict room-temperature lattice thermal conductivities of 75.9 +/- 5.0 W m(-1) K-1 and 147 +/- 7.3 W m(-1) K-1, respectively, and estimate effective phonon mean free paths of 16.7 +/- 1.7 nm and 21.4 +/- 1.0 nm for the zigzag and armchair directions. In this case, the anisotropy is attributed to differences in the density of states of low-frequency phonons, with lower group velocities and possibly shorten phonon lifetimes along the zigzag direction. We also observe that when borophene is strained along the armchair direction there is a significant increase in thermal conductivity along that direction. Meanwhile, when the sample is strained along the zigzag direction there is a much smaller increase in thermal conductivity along that direction. For a strain of 8% along the armchair direction the thermal conductivity increases by a factor of 3.5 (250%), whereas for the same amount of strain along the zigzag direction the increase is only by a factor of 1.2 (20%). Our predictions are in agreement with recent first principles results, at a fraction of the computational cost. The simulations shall serve as a guide for experiments concerning mechanical and thermal properties of borophene and related 2D materials.

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