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We present a general microscopic first-principles method to study theCoulomb-interaction-mediated heat transfer in the near field. Using thenonequilibrium Green's function formalism, we derive Caroli formulas for heattransfers between materials with translational invariance. The central physicalquantities are the screened Coulomb potential and the spectrum function ofpolarizability. Within the random phase approximation, we calculate thepolarizability using the linear response density functional theory and obtainthe screened Coulomb potential from a retarded Dyson equation. We show that theheat transfer mediated by the Coulomb interaction is consistent with that ofthe $p$-polarized evanescent waves which dominate the heat transfer in the nearfield. We adopt single-layer graphene as an example to calculate heat transfersbetween two parallel sheets separated by a vacuum gap $d$. Our results show asaturation of heat flux at the extreme near field which is different from thereported $1/d$ dependence for local response functions. The calculated heatflux is up to $5\times10^4$ times more than the black-body limit, and a $1/d^2$dependence is shown at large separations. From the spectrum of energy currentdensity, we infer that the near-field enhancement of heat transfer stems fromelectron transitions around the Fermi energy. With a uniform strain, the heatflux increases for most of the distances while a negative correlation is shownat the moderate field. Our method is valid for inhomogeneous materials in whichthe macroscopic response function used in conventional theory of fluctuationalelectrodynamics would fail at the subnanometer scale.

Generalized first-principles method to study near-field heat transfer mediated by Coulomb interaction