[gmx-users] Constraint and Temperature Drop in NVE

[Johnny Lu]

Hi.

After equilibrating with NVT (for 10,000 steps of 2fs) and then NPT (10,000
steps of 2fs with V-rescale thermostat at 300K), when I run NVE (0.5fs
timesteps) with a harmonic restraint with force constant 4184kJ/mol rad^2,
the temperature then fluctuate around 292 K (
http://oi60.tinypic.com/sni5at.jpg) in gromacs 4.6.6.

When I instead run NVE with same setting except without the constraint
after the two equilibration steps, the temperature stays around 300K.

What is the cause of this drop of temperature to 292K?

Thanks again.