  We calculate thermal fluctuation properties: volume-averaged order parameter,
Helmholtz free and internal energies, and their variances of a supersaturated
disordered phase in the Gibbs canonical ensemble for an asymmetric (third-order
interactions), athermal (independence of the supersaturation and thermal noise)
effective Hamiltonian. These properties are different from those of the
symmetric thermal one with the most important differences being the phase
coexistence and "thermal expansion." The fluctuation properties of the system
were calculated theoretically, using the perturbation method, and numerically,
using the "brute force" simulations method. Overall, the numerical calculations
match the theory within the accuracy of the numerical method. However, a
discrepancy of the dependence of the internal energy and its variance on the
supersaturation exists. Results of the present study can be used for
calculations of the fluctuation properties of the systems and modeling of
nucleation and other rare events in the framework of the Ginzburg-Landau
method.
