Optimization of Monolayer MoS2 with Prescribed Mechanical Properties

Abstract

Various technological challenges are essentially material problems in our times. New functional and functional graded nanomaterials are constructed of components with predefined properties. The design of nanostructures with predefined mechanical properties was considered in this paper. This study applies the evolutionary algorithm (EA) to the optimization problem in the design of nanomaterials. The optimal design combined EA with molecular dynamics to identify the size of the void for the prescribed elastic properties in monolayer 2D MoS₂ nanostructures. The numerical results show that the proposed EA and the use of optimization method allowed accurately obtaining nanostructures with predefined mechanical material properties by introducing elliptical voids in the 2D MoS₂ nanosheets.

Keywords: MoS2; mechanical properties; nanostructure; optimization.

Figure 1

The nanostructure with an elliptical void described by two design variables.

Figure 2

Determination of nanostructure stiffness in two directions. An ellipse is introduced into the pristine nanostructure by removing atoms in black area. Next, the structure is relaxed, and two analyses of microstructure stretching are performed in two different directions. Then, the stiffness is computed on the basis of the MD results.

Figure 3

Examples of stress-strain relationship during uniaxial tension in two directions.

Figure 4

Evolutionary algorithm flowchart.

Figure 5

Progress of the convergence of the objective function indicating the evolution of the void during iterative generations for prescribed elastic properties P_ref11 = 160 GPa, P_ref22 = 160 GPa. The corresponding void dimensions obtained during generations were (i) g₁ = 46.06 Å and g₂ = 2.95 Å, (ii) g₁ = 32.18 Å and g₂ = 6.07 Å, (iii) g₁ = 33.92 Å and g₂ = 8.86 Å, (iv) g₁ = 21.36 Å and g₂ = 14.88 Å, (v) g₁ = 18.41 Å and g₂ = 19.38 Å, and (vi) g₁ = 28.12 Å and g₂ = 23.15 Å.

Figure 6

Monolayer MoS₂ nanosheet with void identified by optimization: (a) P_ref11 = 180, P_ref22 = 150 GPa (g₁ = 15.35 Å and g₂ = 33.44 Å); (b) P_ref11 = 160, P_ref22 = 160 GPa (g₁ = 28.12 Å and g₂ = 23.15 Å); (c) P_ref11 = 150, P_ref22 = 180 GPa (g₁ = 36.35 Å and g₂ = 12.19 Å).