I found something very surprising when running NPT ensemble both with the  Berendsen  or Martyna-Tobias-Klein thermostat.   I found only fluctuations in the the three principal axes but not the off diagonal matrix elements?  I am using the following CONTROL file.  Did I made any mistake?  I found a simple problem with the test input for water with the DLPOLY package as well,

John

222-768-ice

integration  verlet leapfrog

# System state information
temperature      80.00
pressure         1.000

# Ensemble specification
#ensemble npt berendsen 0.5 1.5
ensemble npt mtk 0.8 5.0


# Startup options

# Simulation controls
timestep          0.001
steps            150000
equilibration      5000
scale                10
print                10
stack               100
stats                10
trajectory          100      10       0
rdf                 100
print rdf
print vaf


# Force cut-offs and controls
cutoff           10.00
rvdw cutoff      10.00

# Electrostatics controls
ewald precision  1.0E-6
shake           1.0E-6

# Job running time and closedown time
job time         100000.00
close time       10.000

finish





John S. Tse, Ph.D, D.Sc, FRS Canada
University Distinguished Professor
University of Saskatchewan Centennial Enhancement Chair
Canada Research Chair in Materials Science (2004-2018)
Department of Physics
116 Science Place
University of Saskatchewan
Saskatoon SK, S7N 5B2 Canada
Tel: (306) 966 6410

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