Interface Conductance Modal Analysis (ICMA)

The interface conductance modal analysis (ICMA) method is a formalism we developed to enable the study of phonon transport at interfaces. In essence it is based on the same underlying principle as GKMA, but here it is reformulated for an interface. One of the most interesting things about ICMA is that it treats the problem of phonon transport at an interface in terms of correlation rather than scattering. This is distinctly different from the predominant physical picture that has been used for many decades. While developing ICMA we realized that you have to perform a full super cell lattice dynamics calculation of a combined structure containing both materials to find the right normal modes needed to describe what happens at the interface. What was surprising though, was that different types of modes exist, namely extended modes, partially extended modes, interfacial modes and isolated modes. These new classifications have prompted a rethinking of the more widely accepted physical picture, as our papers have shown a number of non-intuitive behaviors are possible within our new ICMA based paradigm.

  • The interface conductance modal analysis (ICMA) method works by first calculating the net heat flow across an interface at a given instant during a molecular dynamics simulation. The heat flow is determined from the product of the forces between atoms on the two sides of the interface and their respective velocities. This net heat flow is then tracked over time and the degree to which it remains correlated in time is proportional to the interface conductance between the two groups of atoms. The key advancement of ICMA, however, is in the fact that it provides the normal mode level details of such a calculation, by enabling us to calculate each individual mode’s contribution to the interface conductance.