The equation of state of a homogeneous two-dimensional Bose gas is calculated
using quantum Monte Carlo methods. The low-density universal behavior is
investigated using different interatomic model potentials, both finite-ranged
and strictly repulsive and zero-ranged supporting a bound state. The condensate
fraction and the pair distribution function are calculated as a function of the
gas parameter, ranging from the dilute to the strongly correlated regime. In
the case of the zero-range pseudopotential we discuss the stability of the
gas-like state for large values of the two-dimensional scattering length, and
we calculate the critical density where the system becomes unstable against
cluster formation.Comment: 6 pages, 5 figures, 1 tabl
