FG-MD is a molecular dynamics (MD) based algorithm for high-resolution protein structure refinement. Given an initial protein or protein complex 3D model (either in C-alpha or full-atom), FG-MD first identifies analogous fragments from the PDB by the structural alignment program TM-align. Spatial restraints extracted from the fragments are then used to guide the molecular dynamics simulations. In general, FG-MD aims to refine the initial models closer to the native structure. It also improves the local geometry of the structures by removing the steric clashes and improving the torsion angle and the hydrogen-binding networks. Registration not required.