Thermal properties of graphene from path-integral simulations

Area of Science:

• Condensed matter physics
• Materials science
• Computational physics

Background:

• Graphene's unique thermal properties are crucial for its applications.
• Understanding these properties requires accounting for quantum and anharmonic effects.

Purpose of the Study:

• To investigate the thermal properties of graphene monolayers using advanced simulation techniques.
• To compare simulation results with harmonic approximations across a wide temperature range.

Main Methods:

• Path-integral molecular dynamics (PIMD) simulations.
• Utilizing the LCBOPII effective potential for interatomic interactions.
• Simulations conducted from 12 K to 2000 K under zero external stress.

Main Results:

• PIMD accurately captures anharmonic effects and vibrational mode quantization.
• Harmonic approximation is precise up to 400 K; deviations increase at higher temperatures.
• Thermal expansion coefficient of the real surface area is always positive.
• In-plane thermal expansion coefficient is negative at low temperatures, becoming positive above 1000 K.

Conclusions:

• Anharmonic effects and thermal expansion significantly influence graphene's thermal properties at elevated temperatures.
• The distinction between in-plane and real surface area thermal expansion is critical.
• Accurate modeling requires methods like PIMD beyond simple harmonic approximations for high-temperature behavior.