CCL:convergence of MD simulations



Sue Heavner writes:
  > Dear CCL members:
  >  I read that in NVE simulations, the ratio of RMS fluctuations of
  >  the potential and kinetic energies is an indication
  > of convergence of energy, with RMS(PE)/RMS(KE) = 0.01 indicating a
  > satisfactory level of global energy stabilization.  Is there such a
  > test for NTP simulations?
 If you are using a Hamiltonian-derived set of equations for the NTP
 simulation (such as Nose/Parrinello-Rahman or Nose/Andersen) then the
 answer is yes -- just use the conserved Hamiltonian in place of the
 energy.
 Note that you can't do this directly for the common Nose-Hoover
 formulation, though Frenkel and Smit (p139) suggest a way of
 reconstructing a conserved quantity with a little extra work in
 solving for the s variable.
 Keith Refson
 --
 Dr Keith Refson,
 Building R3
 Rutherford Appleton Laboratory
 Chilton
 Didcot
 Oxfordshire OX11 0QX
 T: 01235 446652		K.Refson[ AT ]
 F: 01235 445720		[ AT ]rl.ac.uk