Polymer folding via external potentials in ab-initio calculations

- External potentials in ab-initio calculations can induce the folding of polymers.
- A general Langevin equation of motion is deduced with an external potential.
- The results of a model polymer are in agreement with molecular mechanics.
- The approach shows great promises for investigating the folding of proteins.
- The approach is compatible with the new computer technologies.

A general method based on the Zwanzig-Langevin approach is provided to investigate the folding of biological or synthetic polymers. The method departs from a Lagrangian for a molecule inside a fluid (liquid or gas), and subject to an external potential. The equations of motion are deduced and solved by considering the statistical nature of the fluid. We study different external potentials capable of inducing the folding. The results on a model polymer (polyethylene) are very promising since several minima close in energy are distinguished for very different molecular conformations. The external potentials not only facilitate the folding, but also provide an alternative for rapidly determining the energetically stable structures.