OLD Langevin Dynamics

Description of Langevin Dynamics
Langevin dynamics (LD) is similar to molecular dynamics (MD) simulations except the LD simulations apply frictional forces to the atoms. In self-guided Langevin dynamics (SGLD), there is also a guiding force, which is a momentum-derived force that pushes atoms. Because of this factor, more conformations will be sampled in a given interval and thus it should only be used if the timescale

Basic Langevin Dynamics Script
Please read the Basic MD Script section before continuing on the Langevin Dynamics. The "DYNA" command is used to run both Langevin dynamics and molecular dynamics, so the script will look similar to that one.

Before starting the "DYNA" command, the friction coefficient (expressed as collisions per picosecond) must be read in by CHARMM. This tutorial will use a value of 60 (the approximate collision frequency of water at room temperature). "SCALar FBETa SET 60.0 SELEct ALL END" will apply the friction force to the entire system.

Using the same MD script as in the molecular dynamics tutorial, change the "DYNA" command by adding "LANG" after "DYNA". The "SGLD" subcommand should be used for SGLD.

Langevin dynamics should not be used with constant pressure and temperature (CPT) so change "CPT" to "LEAP". Since the "PCONS" and "HOOVer" subcommands are related to CPT, remove them. Langevin dynamics has its own temperature control so the Nose-Hoover thermostat is not required.

The input script should look like the following: