  Hybrid organic-inorganic perovskites (HOIP) have emerged in recent years as
highly promising semiconducting materials for a wide range of optoelectronic
and energy applications. Nevertheless, the rotational dynamics of the organic
components and many molecule interdependencies, which may strongly impact the
functional properties of HOIP, are not yet fully understood. In this study, we
quantitatively analyze the orientational disorder and molecular correlations in
the archetypal perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ (MAPI) by performing
comprehensive molecular dynamics simulations and entropy calculations. We found
that, in addition to the usual vibrational and orientational contributions,
rigid molecular rotations around the C-N axis and correlations between
neighboring molecules noticeably contribute to the entropy increment associated
with the temperature-induced order-disorder phase transition in MAPI, $\Delta
S_{t}$. Molecular conformational changes are equally infrequent in the low-$T$
ordered and high-$T$ disordered phases and have a null effect on $\Delta
S_{t}$. Conversely, the couplings between the angular and vibrational degrees
of freedom are substantially reinforced in the high-$T$ disordered phase and
significantly counteract the phase-transition entropy increase resulting from
other factors. Furthermore, the tendency for neighboring molecules to be
orientationally ordered is markedly local, consequently inhibiting the
formation of extensive polar nanodomains both at low and high temperatures.
This theoretical investigation not only advances the fundamental knowledge of
HOIP but also establishes physically insightful connections with contemporary
technological applications like photovoltaics and solid-state cooling.
