  Interactions of molecules with their environment influence the course and
outcome of almost all chemical reactions. However, classical computers struggle
to accurately simulate complicated molecule-environment interactions because of
the steep growth of computational resources with both molecule size and
environment complexity. Therefore, many quantum-chemical simulations are
restricted to isolated molecules, whose dynamics can dramatically differ from
what happens in an environment. Here, we show that analog quantum simulators
can simulate open molecular systems by using the native dissipation of the
simulator and injecting additional controllable dissipation. By exploiting the
native dissipation to simulate the molecular dissipation -- rather than seeing
it as a limitation -- our approach enables longer simulations of open systems
than are possible for closed systems. In particular, we show that trapped-ion
simulators using a mixed qudit-boson (MQB) encoding could simulate molecules in
a wide range of condensed phases by implementing widely used dissipative
processes within the Lindblad formalism, including pure dephasing and both
electronic and vibrational relaxation. The MQB open-system simulations require
significantly fewer additional quantum resources compared to both classical and
digital quantum approaches.
