  Accounting for electrons and nuclei simultaneously is a powerful capability
of ab initio molecular dynamics (AIMD). However, AIMD is often unable to
accurately reproduce properties of systems such as water due to inaccuracies in
the underlying electronic density functionals. This shortcoming is often
addressed by added empirical corrections and/or increasing the simulation
temperature. We present here a maximum-entropy approach to directly incorporate
limited experimental data via a minimal bias. Biased AIMD simulations of water
and an excess proton in water are shown to give significantly improved
properties both for observables which were biased to match experimental data
and for unbiased observables. This approach also yields new physical insight
into inaccuracies in the underlying density functional theory as utilized in
the unbiased AIMD.
