  We present MIST, the Molecular Integration Simulation Toolkit, a lightweight
and efficient software library written in C++ which provides an abstract in-
terface to common molecular dynamics codes, enabling rapid and portable
development of new integration schemes for molecular dynamics. The initial
release provides plug-in interfaces to NAMD-Lite, GROMACS and Amber, and
includes several standard integration schemes, a constraint solver, tem-
perature control using Langevin Dynamics, and two tempering schemes. We
describe the architecture and functionality of the library and the C and For-
tran APIs which can be used to interface additional MD codes to MIST. We show,
for a range of test systems, that MIST introduces negligible overheads for
serial, shared-memory parallel, and GPU-accelerated cases, except for Amber
where the native integrators run directly on the GPU itself. As a demonstration
of the capabilities of MIST, we describe a simulated tempering simulation used
to study the free energy landscape of Alanine-12 in both vacuum and detailed
solvent conditions.
