Online Simulations Via Nanohub: Nanoscale Thermal Transport Via MD

Online simulations via nanoHUB: Nanoscale thermal transport via MD

In this tutorial: • Non-equilibrium MD simulations of thermal transport

Keng-hua Lin and Ale Strachan [email protected] School of Materials Engineering & Birck Nanotechnology Center Purdue University West Lafayette, Indiana USA

• Launch tool by clicking on:

• Select prebuilt structures

• Or create your own structure by checking the box

We will create our own

© Alejandro Strachan – Online simulaons: geng started 3 How the simulation cells are defined • Along the transport direcon the simulaon contains: • 2 Heat baths (blue) • The middle bin deﬁnes the hot and cold regions • Interior material (red) • This can be deﬁned to be a superlace • Periodic boundary condions are applied along the transport direcon Material (5 bins) Heat bath (3 bins)

Cold bin Hot bin

F. Müller-Plathe, J. Chem. Phys. 106, 6082 (1997) Keng-Hua Lin and A. Strachan, Physical Review B, 87, 115302 (2013).

• We would like to create a Si supercell by replicang the cubic Si unit cell • The tool allows users to build superlaces (laminates) so it is a bit convoluted

Along the transport the system will be divided in bins Each bin is one unit cell long

Cross-seconal area of the simulaon cell (5x5 unit cells) Lace parameter (5.43) Along the transport direcon the “supercell” will have 5 Si bins (1 bin = 1 unit cell) and zero Ge (just Si) The number of Si bins will be varied to explore size eﬀects The total simulaon length in this case is: (3+5) x 2 x 5.43A = 86.88A The eﬀecve size for transport is the separaon between heat baths (1/2 of the simulaon cell length)

Heat baths are 3 bins long The “supercell” will be repeated only once

If you select to build your own structure In the Selecons for Material Shape tab Choose to simulate the material as a bulk (superlace thin ﬁlm) or a superlace square nanowire

3-D periodic boundary condion for the simulaon cell

Periodic boundary condion along the z direcon and free boundary condion along the x and y direcons

We will use 3D periodic boundary condions

From the Driver Speciﬁcaon tab of the tool

Thermalize the system

For 1000 MD steps (2 ps)

This will equilibrate the system to the desired temperature before starng the thermal transport calculaon

Timestep 2 fs

MD steps 120,000

Swap atomic velocies every 100 MD steps

Atomisc snapshots for visualizaon

Output temperature proﬁle every this many steps for analysis

Ignore the ﬁrst 20,000 steps when compung averages

Temperature proﬁles at diﬀerent mes

Average temperature proﬁle

Remember simulaon cell was ~86A

Analyze output: calculated thermal conducvity

Material thermal conducvity computer from temperature gradient inside the material (away from contacts) Use this value