MODEL FERMION MONTE-CARLO WITH CORRELATED PAIRS .2.

We study the fundamental challenge of fermion Monte Carlo for continuo us systems: the fermion ''sign problem.'' In particular, we describe m ethods that depend upon the use of correlated dynamics for ensembles o f correlated sets of walkers that carry opposite signs. We explain the concept of marginally correct dynamics, and show that marginally corr ect dynamics that produce a stable overlap with an antisymmetric trial function give the correct fermion ground state. Many-body harmonic os cillator problems are particularly tractable: their stochastic dynamic s permits the use of regular geometric structures for the ensembles, s tructures that are stable when appropriate correlations are introduced , and avoid the decay of signal-to-noise that is a normal characterist ic of the sign problem. This approach may be a guide in the search for algorithmic approaches to calculations of physical interest.