Hamiltonian Thermostats Fail to Promote Heat Flow

TL;DR

Hamiltonian thermostats, when used to impose different temperatures in a composite system, do not facilitate heat flow, indicating that steady heat transfer requires energy sources and sinks outside Hamiltonian mechanics.

Contribution

This paper demonstrates that Hamiltonian thermostats cannot promote heat flow between regions at different temperatures, challenging their use in modeling steady heat transfer.

Findings

Hamiltonian thermostats do not induce heat flow between hot and cold regions.

Steady heat transfer requires energy sources and sinks outside Hamiltonian frameworks.

Hamiltonian models are incompatible with simulating continuous heat flow.

Abstract

Hamiltonian mechanics can be used to constrain temperature simultaneously with energy. We illustrate the interesting situations that develop when two different temperatures are imposed within a composite Hamiltonian system. The model systems we treat are "phi-4" chains, with quartic tethers and quadratic nearest-neighbor Hooke's-law interactions. This model is known to satisfy Fourier's law. Our prototypical problem sandwiches a Newtonian subsystem between hot and cold Hamiltonian reservoir regions. We have characterized four different Hamiltonian reservoir types. There is no tendency for any of these two-temperature Hamiltonian simulations to transfer heat from the hot to the cold degrees of freedom. Evidently steady heat flow simulations require energy sources and sinks, and are therefore incompatible with Hamiltonian mechanics.