  Thermal radiative phenomena can be strongly influenced by the coupling of
phonons and long-range electromagnetic fields at infrared frequencies.
Typically employed macroscopic descriptions of thermal fluctuations tend to
ignore atomistic effects that become relevant at nanometric scales, whereas
purely microscopic treatments ignore long-range, geometry-dependent
electromagnetic effects. We describe a mesoscopic framework for modeling
thermal fluctuation phenomena among molecules in the vicinity of macroscopic
bodies, conjoining atomistic treatments of electronic and vibrational
fluctuations obtained from ab-initio density functional theory in the former
with continuum descriptions of electromagnetic scattering in the latter. The
interplay of these effects becomes particularly important at mesoscopic scales,
where phonon polaritons can be strongly influenced by the finite sizes, shapes,
and non-local/many-body response of the bodies to electromagnetic fluctuations.
We show that even in small but especially in elongated low-dimensional
molecular systems, such effects can modify thermal emission and heat transfer
by orders of magnitude and produce qualitatively different behavior compared to
predictions based on local, dipolar, or pairwise approximations valid only in
dilute media.
