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Starting from Monte Carlo generated equilibrium gauge field configurations at fl = 2.1 and 2.2 on a 64 lattice, representing the physical vacuum, we systematically freeze the quantum fluctuations by means of successive relaxations. The result is that we obtain (approximate) solutions of the classical equations of motion, which turn out to have discrete values of the action S'~fl2~r2N, N=0,1,2 ..... in close agreement with the continuum (multi-) instanton solutions. We show that these "lattice (multi-) instantons" are localized in space-time, that they carry a topological charge IQ1 = N and that they give rise to a number of fermion zero modes in accordance with the Atiyah-Singer index theorem. Finally, we estimate the "background topological susceptibility" from the distribution of lattice (multi-) instantons.

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We present a multicanonical algorithm for the SU(3) pure gauge theory at the deconfinement phase transition. We measure the tunneling times for lattices of size L 3 ×2 for L = 8, 10, and 12. In contrast to the canonical algorithm the tunneling time increases only moderately with L. Finally, we determine the interfacial free energy applying the multicanonical algorithm.