  We investigate the ground state properties of one-dimensional hard-core
bosons interacting via a variable long-range potential using the density matrix
renormalization group. We demonstrate that restoring energy extensivity in the
system, which is done by rescaling the interaction potential with a suitable
size-dependent factor known as Kac's prescription, has a profound influence on
the low-energy properties in the thermodynamic limit. While an insulating phase
is found in the absence of Kac's rescaling, the latter leads to a new metallic
phase that does not fall into the conventional Luttinger liquid paradigm. Our
results in one dimension illustrate the subtlety of determining the
thermodynamic properties of generic long-range quantum systems.
