Langevin dynamics implementation

[SHervoe-Hansen]

The implementation of Langevin dynamics in Faunus for a Lennard-Jones fluid/gas is well underway in my fork of Faunus. Checklist which should preferably be handled as separate PRs:

• Working example of LJ system
• Unit testing
  • simple LJ system. RDF, temperature, avg. kinetic and potential energy? Compare w. MC
  • harmonic oscillator?
• Force calculation implementation:
  • Force calculation for Ewald summation scheme #284: Reciprocal ewald space
  • Force calculation for bonded interactions #283: Bonded interactions (harmonic, torsion, dihedrals -- see OpenMM implementation) and also Allen+Tildesley, Appendix C
  • FunctorPotential for combined potentials
  • Anisotropic non-bonded interactions?
  • See Allen and Tildesley's Appendix C as well as their Github rep with examples of force calculations (ewald, angles, dipoles etc.)
• Error handling
  • Gracefully exit from explosion (closes Error running example langevin_lj.yml #305)
• Documentation (moves.md)
• An initialisation scheme for simulation of liquids (slow heating, minimisation using 0 K Monte Carlo).
• Improved control over MD/MC switching.
• Parallel scheme for force calculation in Nonbonded class (OMP pragmas?)

[udayardahal]

Is it possible for me to get the beta version of the code where you have implemented langevin dynamics? I want to test CG martini system ( I don't have any angle/dihedral terms in the system).
Thanks,