Simulating a tribological system with accuracy is a formidable difficult task. To provide a quantitative estimate of the kinetic friction coefficient, one should in fact rely on a multiscale approach that includes both the electronic degrees of freedom of the interface and the elastic properties of the semi-infinite bulks. Ab initio molecular dynamics (AIMD) simulations provide a reliable description of the chemical interactions at the sliding interface but cannot be used to obtain quantitative estimates of the energy dissipation by phonons because of the use of slabs of finite thickness. Another problematic issue is related to the realistic pressure and temperature control in non-equilibrium conditions. Green’s function MD (GFMD) constitutes an elegant way to overcome these limitations [1,2], because it implicitly includes the influence of the infinite bulk atoms on the dynamics of surface atoms. This projection of the semi-infinite degrees of freedom allows representing the phonon energy dissipation and thermo/baro-stats in a well-defined manner [3].

Here we present an innovative procedure to link GFMD to AIMD, realizing an AIMD/GFMD hybrid model able to describe the reactive friction interface with the high accuracy of quantum mechanics and at the same time include the proper control of temperature, mechanical stresses, and energy dissipation in non-equilibrium conditions. We adopted it to study the sliding interface between two H-terminated diamond surfaces with different degrees of passivation, providing a quantitative estimation of the kinetic friction coefficient [4].

The presented results are part of the "Advancing Solid Interface and Lubricants by First Principles Material Design (SLIDE)" project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant agreement No. 865633).

References

[1] C. Campana and M.H. Muser, Phys. Rev. B 74, 075420 (2006)
[2] L.T. Kong, G. Bartels, C. Campana, C. Denniston, and M.H. Muser, Comput. Phys. Commun. 180, 1004-1010 (2009)
[3] S. Kajita, Phys. Rev. E 94, 033301 (2016)
[4] S. Kajita, G. Losi, N. Kikkawa, and M.C. Righi, in preparation