  The instability strip (IS) of classical Cepheids has been extensively studied
theoretically. Comparison of the theoretical IS edges with those obtained
empirically, using the most recent Cepheids catalogs available, can provide us
with insights into the physical processes that determine the position of the IS
boundaries. In this study, we investigate the empirical positions of the IS of
the classical Cepheids in the Large Magellanic Cloud (LMC), considering any
effect that increases its width, to obtain intrinsic edges that can be compared
with theoretical models. We use data of classical fundamental-mode (F) and
first-overtone (1O) LMC Cepheids from the OGLE-IV variable star catalog,
together with a recent high-resolution reddening map from the literature. Our
final sample includes 2058 F and 1387 1O Cepheids. We studied their position on
the Hertzsprung-Russell diagram and determined the IS borders by tracing the
edges of the color distribution along the strip. We obtain the blue and red
edges of the IS in V- and I-photometric bands, in addition to $\log T_{\rm
eff}$ and $\log L$. The results obtained show a break located at the Cepheids'
period of about 3 days, which was not reported before. We compare our empirical
borders with theoretical ones published in the literature obtaining a good
agreement for specific parameter sets. The break in the IS borders is most
likely explained by the depopulation of second and third crossing classical
Cepheids in the faint part of the IS, since blue loops of evolutionary tracks
in this mass range do not extend blueward enough to cross the IS at the LMC
metallicity. Results from the comparison of our empirical borders with
theoretical ones prove that our empirical IS is a useful tool for constraining
theoretical models.
