Heat transport through a biological membrane—An asymmetric property? Technical issues of nonequilibrium molecular dynamics methods

To investigate heat transport across a biological membrane, we performed a series of reverse nonequilibrium molecular dynamics (RNEMD) simulations on a model dipalmitoylphosphatidylcholine (DPPC) bilayer system at the atomistic level. In a detailed analysis of the initially irritating results, we show how and to which extent the RNEMD method (in the special case of an ordered, heterogeneous system, like a bilayer in water) is influenced by simulation conditions. We prove that the interplay between the description of the long range forces and the nonequilibrium algorithm can lead to significant changes in the apparent local thermal conductivity profile across the membrane. As this is the first case reported where the otherwise robust RNEMD results are not directly interpretable, we discuss not only the reasons but also several concepts to handle this effect. Note that this is not a flaw of the RNEMD method but of the simulation framework it is performed in. Therefore, the considerations apply to other equilibrium and nonequilibrium molecular dynamics simulations of the thermal conductivities, too, and care must be taken when heterogeneous systems or interfaces appear in simulations. The complete understanding of the directly obtained results finally allows us to describe the heat flow across the membrane qualitatively. On this basis, we show that the tail–tail interface of the bilayer is the most hindering region for the heat flow, and thus, dominates the overall thermal conductivity of the membrane. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010