Velocity Scaling and Equilibration

Information about the Velocity Scaling and Equilibrium Interactive Demonstration:

• Simulation uses a Lennard-Jones potential with = 3.41 Angstroms and = 0.0099567 kcal/mole.
• 256 particles of mass 18 amu
• Periodic boundary conditions with cube of side 28 A
• Shifted force, r_c=11 A
• T=300K
• Velocity Verlet algorithm
• For steps 1-3000, t=1 fs
• For steps 3000-6500, t = 0.1 fs

Scale velocities every 500 steps:

• v_new=(T_target/T_instan)^1/2v_old
• T_target=300K
• T_instan=2K/(N_f*k_B)
• v_old: old velocities
• v_new: new velocities
• N_f: number of degrees of freedom (3*256)
• K: instantaneous kinetic energy (for velocities v_old)
• k_B: Boltzmann's constant

Additional Information:

Starting configuration: simple cubic, side 4 A, particle at origin.
Note: This is a very nonequilibrium starting configuration because the particles are not evenly distributed in the system box. Thus, the potential energy decreases as the particles spread out (i.e. equilibrate).