Anharmonic effects on thermodynamic properties of a graphene monolayer

¹ Instituto de Física, Universidade Federal de Goiás - 74001-970, Goiânia, GO, Brazil
² Departamento de Matemática e Física, Pontifícia Universidade Católica de Goiás - 74605-010, Goiânia, GO, Brazil
³ Instituto de Física de São Carlos, Universidade de São Paulo - 13560-970, São Carlos, SP, Brazil
⁴ Departement Fysica, Universiteit Antwerpen - Groenenborgerlaan 171, 2020 Antwerpen, Belgium

Received: 16 July 2014
Accepted: 20 August 2014

Abstract

We extend the unsymmetrized self-consistent-field method (USF) for anharmonic crystals to layered non-Bravais crystals to investigate structural, dynamical and thermodynamic properties of a free-standing graphene monolayer. In this theory, the main anharmonicity of the crystal lattice has been included and the quantum corrections are taken into account in an ℏ-expansion for the one-particle density matrix. The obtained result for the thermal expansion coefficient (TEC) of graphene shows a strong temperature dependence and agrees with experimental results by Bao et al. (Nat. Nanotechnol., 4 (2009) 562). The obtained value of TEC at room temperature (300 K) is and it becomes positive for . We find that quantum effects are significant for . The interatomic distance, effective amplitudes of the graphene lattice vibrations, adiabatic and isothermal bulk moduli, isobaric and isochoric heat capacities are also calculated and their temperature dependences are determined.