Markov state models (MSMs) have been broadly adopted for analyzing molecular
dynamics trajectories, but the approximate nature of the models that results
from coarse-graining into discrete states is a long-known limitation. We show
theoretically that, despite the coarse graining, in principle MSM-like analysis
can yield unbiased estimation of key observables. We describe unbiased
estimators for equilibrium state populations, for the mean first-passage time
(MFPT) of an arbitrary process, and for state committors - i.e., splitting
probabilities. Generically, the estimators are only asymptotically unbiased but
we describe how extension of a recently proposed reweighting scheme can
accelerate relaxation to unbiased values. Exactly accounting for 'sliding
window' averaging over finite-length trajectories is a key, novel element of
our analysis. In general, our analysis indicates that coarse-grained MSMs are
asymptotically unbiased for steady-state properties only when appropriate
boundary conditions (e.g., source-sink for MFPT estimation) are applied
directly to trajectories, prior to calculation of the appropriate transition
matrix.
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Title
Unbiased estimation of equilibrium, rates, and committors from Markov state model analysis