An algorithm is proposed for the simulation of molecular systems with hybrid quantum chemical (QC) and molecular mechanical (MM) potentials that permits the adaptive partitioning of the atoms in the system between QC and MM regions. In contrast to existing methods, the algorithm requires only a single QC calculation of the QC/MM system per energy calculation and yet has consistent energy and forces, which makes it suitable for geometry optimizations and molecular dynamics calculations within the microcanonical ensemble, in addition to other types of simulation. This article describes the algorithm and its implementation, presents some simple test cases with both semiempirical and density functional theory QC/MM potentials, and discusses perspectives for future work.