NVE simulations in DLPOLY Classic 1.10


I am running a polarizable water simulation with a NVE ensemble using tabulated potential. But I am observing total energy is not conserved, after the equilibration period total energy should remain in a certain fluctuation window. Total number of molecules in a box is 256. But it is not behaving in this way. If you want I can show my inputs.

Here is my CONTROL parameters


velocity verlet integration selected

microcanonical ensemble

simulation temperature 2.9815E+02

selected number of timesteps 600000

equilibration period 100000

temperature scaling on
temperature scaling interval 1000

data printing interval 1000

data stacking interval 1000

statistics file interval 1000

trajectory file option on
trajectory file start 100001
trajectory file interval 1000
trajectory file info key 0

border width of Verlet shell 0.0000E+00

radial distribution functions on
g(r) collection interval 500
g(r) bin width 5.0000E-02

g(r) printing option on

data printing interval 1

simulation timestep 1.0000E-03

real space cut off 9.0000E+00

Ewald sum precision 1.0000E-06

Electrostatics : Ewald sum

Ewald convergence parameter 3.5818E-01
Ewald kmax1 kmax2 kmax3 7 7 7

Follow is the behavior of total energy
At 100000 step total energy was -2.2045E+03
and at 400000 step total energy is 3.0091E+02

Which shows it is completely inconsistent with NVE simulation.


firstly I will use 5.0.0 since classic is not really supported...
secondly I will triple check that the forces in the table are consistent with the energy.
of course after I will check the timestep is right for what you are trying to integrate.
ewald cutoff and precision are right for the long range.


Without Questions there are no Answers!

But i have tested NVT simulation also and it is giving sensible results. I can try 5.0.0