Gaussian wavefunctional approach in thermofield dynamics

The Gaussian wavefunctional approach is developed in thermofield dynamics. We construct the thermal vacuum wavefunctional. its creation as well as ann ihilation operators, and accordingly the thermo-panicle excited states. For a (D + 1)-dimensional scalar field system with on arbitrary potential whos e Fourier representation exists in the sense of tempered distributions. we calculate the finite-temperature Gaussian effective potential (FTGEP). one- and two-thermo-particle-state energies. The zero-temperature limit of each of them is just the corresponding result in quantum field theory, and the FTGEP can lend to the same one for some concrete models as calculated by th e imaginary-time Green function.